Use the instrument PenTool to draw the mailbox's cover. Use the indicated parameters:

Illustration of a Mailbox in Photoshop

Blending Options-Gradient Overlay

Illustration of a Mailbox in Photoshop

Gradient's parameters

Illustration of a Mailbox in Photoshop

Blending Options-Stroke

Illustration of a Mailbox in Photoshop

Take the instrument PenTool and draw a part of the mailbox's cover. The parameters are shown:

Illustration of a Mailbox in Photoshop

Blending
 
Options-Gradient Overlay

Illustration of a Mailbox in Photoshop

Gradient's parameters

Illustration of a Mailbox in Photoshop

Blending Options-Stroke

Illustration of a Mailbox in Photoshop

Use the previous instrument to make a part of the mailbox's cover with the indicated parameters below:

Illustration of a Mailbox in Photoshop

Blending Options-Gradient Overlay

Illustration of a Mailbox in Photoshop