diff --git a/openstack/blockstorage/v1/volumes/requests.go b/openstack/blockstorage/v1/volumes/requests.go
index bca27db..dc04732 100644
--- a/openstack/blockstorage/v1/volumes/requests.go
+++ b/openstack/blockstorage/v1/volumes/requests.go
@@ -1,62 +1,93 @@
 package volumes
 
 import (
+	"fmt"
+
 	"github.com/rackspace/gophercloud"
 	"github.com/rackspace/gophercloud/pagination"
 
 	"github.com/racker/perigee"
 )
 
+// CreateOptsBuilder allows extensions to add additional parameters to the
+// Create request.
+type CreateOptsBuilder interface {
+	ToVolumeCreateMap() (map[string]interface{}, error)
+}
+
 // CreateOpts contains options for creating a Volume. This object is passed to
 // the volumes.Create function. For more information about these parameters,
 // see the Volume object.
 type CreateOpts struct {
-	Availability                     string            // OPTIONAL
-	Description                      string            // OPTIONAL
-	Metadata                         map[string]string // OPTIONAL
-	Name                             string            // OPTIONAL
-	Size                             int               // REQUIRED
-	SnapshotID, SourceVolID, ImageID string            // REQUIRED (one of them)
-	VolumeType                       string            // OPTIONAL
+	// OPTIONAL
+	Availability string
+	// OPTIONAL
+	Description string
+	// OPTIONAL
+	Metadata map[string]string
+	// OPTIONAL
+	Name string
+	// REQUIRED
+	Size int
+	// OPTIONAL
+	SnapshotID, SourceVolID, ImageID string
+	// OPTIONAL
+	VolumeType string
+}
+
+// ToVolumeCreateMap assembles a request body based on the contents of a
+// CreateOpts.
+func (opts CreateOpts) ToVolumeCreateMap() (map[string]interface{}, error) {
+	v := make(map[string]interface{})
+
+	if opts.Size == 0 {
+		return nil, fmt.Errorf("Required CreateOpts field 'Size' not set.")
+	}
+	v["size"] = opts.Size
+
+	if opts.Availability != "" {
+		v["availability_zone"] = opts.Availability
+	}
+	if opts.Description != "" {
+		v["display_description"] = opts.Description
+	}
+	if opts.ImageID != "" {
+		v["imageRef"] = opts.ImageID
+	}
+	if opts.Metadata != nil {
+		v["metadata"] = opts.Metadata
+	}
+	if opts.Name != "" {
+		v["display_name"] = opts.Name
+	}
+	if opts.SourceVolID != "" {
+		v["source_volid"] = opts.SourceVolID
+	}
+	if opts.SnapshotID != "" {
+		v["snapshot_id"] = opts.SnapshotID
+	}
+	if opts.VolumeType != "" {
+		v["volume_type"] = opts.VolumeType
+	}
+
+	return map[string]interface{}{"volume": v}, nil
 }
 
 // Create will create a new Volume based on the values in CreateOpts. To extract
-// the Volume object from the response, call the Extract method on the CreateResult.
-func Create(client *gophercloud.ServiceClient, opts *CreateOpts) CreateResult {
-
-	type volume struct {
-		Availability *string           `json:"availability_zone,omitempty"`
-		Description  *string           `json:"display_description,omitempty"`
-		ImageID      *string           `json:"imageRef,omitempty"`
-		Metadata     map[string]string `json:"metadata,omitempty"`
-		Name         *string           `json:"display_name,omitempty"`
-		Size         *int              `json:"size,omitempty"`
-		SnapshotID   *string           `json:"snapshot_id,omitempty"`
-		SourceVolID  *string           `json:"source_volid,omitempty"`
-		VolumeType   *string           `json:"volume_type,omitempty"`
-	}
-
-	type request struct {
-		Volume volume `json:"volume"`
-	}
-
-	reqBody := request{
-		Volume: volume{},
-	}
-
-	reqBody.Volume.Availability = gophercloud.MaybeString(opts.Availability)
-	reqBody.Volume.Description = gophercloud.MaybeString(opts.Description)
-	reqBody.Volume.ImageID = gophercloud.MaybeString(opts.ImageID)
-	reqBody.Volume.Name = gophercloud.MaybeString(opts.Name)
-	reqBody.Volume.Size = gophercloud.MaybeInt(opts.Size)
-	reqBody.Volume.SnapshotID = gophercloud.MaybeString(opts.SnapshotID)
-	reqBody.Volume.SourceVolID = gophercloud.MaybeString(opts.SourceVolID)
-	reqBody.Volume.VolumeType = gophercloud.MaybeString(opts.VolumeType)
-
+// the Volume object from the response, call the Extract method on the
+// CreateResult.
+func Create(client *gophercloud.ServiceClient, opts CreateOptsBuilder) CreateResult {
 	var res CreateResult
+
+	reqBody, err := opts.ToVolumeCreateMap()
+	if err != nil {
+		res.Err = err
+		return res
+	}
+
 	_, res.Err = perigee.Request("POST", createURL(client), perigee.Options{
 		MoreHeaders: client.Provider.AuthenticatedHeaders(),
-		ReqBody:     &reqBody,
+		ReqBody:     reqBody,
 		Results:     &res.Resp,
 		OkCodes:     []int{200, 201},
 	})
@@ -72,8 +103,8 @@
 	return err
 }
 
-// Get retrieves the Volume with the provided ID. To extract the Volume object from
-// the response, call the Extract method on the GetResult.
+// Get retrieves the Volume with the provided ID. To extract the Volume object
+// from the response, call the Extract method on the GetResult.
 func Get(client *gophercloud.ServiceClient, id string) GetResult {
 	var res GetResult
 	_, res.Err = perigee.Request("GET", getURL(client, id), perigee.Options{
@@ -84,66 +115,101 @@
 	return res
 }
 
+// ListOptsBuilder allows extensions to add additional parameters to the List
+// request.
+type ListOptsBuilder interface {
+	ToVolumeListParams() (string, error)
+}
+
 // ListOpts holds options for listing Volumes. It is passed to the volumes.List
 // function.
 type ListOpts struct {
-	AllTenants bool              `q:"all_tenants"` // admin-only option. Set it to true to see all tenant volumes.
-	Metadata   map[string]string `q:"metadata"`    // List only volumes that contain Metadata.
-	Name       string            `q:"name"`        // List only volumes that have Name as the display name.
-	Status     string            `q:"status"`      // List only volumes that have a status of Status.
+	// admin-only option. Set it to true to see all tenant volumes.
+	AllTenants bool `q:"all_tenants"`
+	// List only volumes that contain Metadata.
+	Metadata map[string]string `q:"metadata"`
+	// List only volumes that have Name as the display name.
+	Name string `q:"name"`
+	// List only volumes that have a status of Status.
+	Status string `q:"status"`
+}
+
+// ToVolumeListParams formats a ListOpts into a query string.
+func (opts ListOpts) ToVolumeListParams() (string, error) {
+	q, err := gophercloud.BuildQueryString(opts)
+	if err != nil {
+		return "", err
+	}
+	return q.String(), nil
 }
 
 // List returns Volumes optionally limited by the conditions provided in ListOpts.
-func List(client *gophercloud.ServiceClient, opts *ListOpts) pagination.Pager {
+func List(client *gophercloud.ServiceClient, opts ListOptsBuilder) pagination.Pager {
 	url := listURL(client)
 	if opts != nil {
-		query, err := gophercloud.BuildQueryString(opts)
+		query, err := opts.ToVolumeListParams()
 		if err != nil {
 			return pagination.Pager{Err: err}
 		}
-		url += query.String()
+		url += query
 	}
 	createPage := func(r pagination.LastHTTPResponse) pagination.Page {
 		return ListResult{pagination.SinglePageBase(r)}
 	}
-	return pagination.NewPager(client, listURL(client), createPage)
+	return pagination.NewPager(client, url, createPage)
+}
+
+// UpdateOptsBuilder allows extensions to add additional parameters to the
+// Update request.
+type UpdateOptsBuilder interface {
+	ToVolumeUpdateMap() (map[string]interface{}, error)
 }
 
 // UpdateOpts contain options for updating an existing Volume. This object is passed
 // to the volumes.Update function. For more information about the parameters, see
 // the Volume object.
 type UpdateOpts struct {
-	Name        string            // OPTIONAL
-	Description string            // OPTIONAL
-	Metadata    map[string]string // OPTIONAL
+	// OPTIONAL
+	Name string
+	// OPTIONAL
+	Description string
+	// OPTIONAL
+	Metadata map[string]string
+}
+
+// ToVolumeUpdateMap assembles a request body based on the contents of an
+// UpdateOpts.
+func (opts UpdateOpts) ToVolumeUpdateMap() (map[string]interface{}, error) {
+	v := make(map[string]interface{})
+
+	if opts.Description != "" {
+		v["display_description"] = opts.Description
+	}
+	if opts.Metadata != nil {
+		v["metadata"] = opts.Metadata
+	}
+	if opts.Name != "" {
+		v["display_name"] = opts.Name
+	}
+
+	return map[string]interface{}{"volume": v}, nil
 }
 
 // Update will update the Volume with provided information. To extract the updated
 // Volume from the response, call the Extract method on the UpdateResult.
 func Update(client *gophercloud.ServiceClient, id string, opts *UpdateOpts) UpdateResult {
-	type update struct {
-		Description *string           `json:"display_description,omitempty"`
-		Metadata    map[string]string `json:"metadata,omitempty"`
-		Name        *string           `json:"display_name,omitempty"`
-	}
-
-	type request struct {
-		Volume update `json:"volume"`
-	}
-
-	reqBody := request{
-		Volume: update{},
-	}
-
-	reqBody.Volume.Description = gophercloud.MaybeString(opts.Description)
-	reqBody.Volume.Name = gophercloud.MaybeString(opts.Name)
-
 	var res UpdateResult
 
+	reqBody, err := opts.ToVolumeUpdateMap()
+	if err != nil {
+		res.Err = err
+		return res
+	}
+
 	_, res.Err = perigee.Request("PUT", updateURL(client, id), perigee.Options{
 		MoreHeaders: client.Provider.AuthenticatedHeaders(),
 		OkCodes:     []int{200},
-		ReqBody:     &reqBody,
+		ReqBody:     reqBody,
 		Results:     &res.Resp,
 	})
 	return res
diff --git a/openstack/blockstorage/v1/volumes/requests_test.go b/openstack/blockstorage/v1/volumes/requests_test.go
index d1632d1..7cd37d5 100644
--- a/openstack/blockstorage/v1/volumes/requests_test.go
+++ b/openstack/blockstorage/v1/volumes/requests_test.go
@@ -119,7 +119,7 @@
 		th.TestJSONRequest(t, r, `
 {
     "volume": {
-        "display_name": "vol-001"
+        "size": 4
     }
 }
 			`)
@@ -130,18 +130,18 @@
 		fmt.Fprintf(w, `
 {
     "volume": {
-        "display_name": "vol-001",
+        "size": 4,
         "id": "d32019d3-bc6e-4319-9c1d-6722fc136a22"
     }
 }
 		`)
 	})
 
-	options := &CreateOpts{Name: "vol-001"}
+	options := &CreateOpts{Size: 4}
 	n, err := Create(ServiceClient(), options).Extract()
 	th.AssertNoErr(t, err)
 
-	th.AssertEquals(t, n.Name, "vol-001")
+	th.AssertEquals(t, n.Size, 4)
 	th.AssertEquals(t, n.ID, "d32019d3-bc6e-4319-9c1d-6722fc136a22")
 }