On Wed, 3 Jul 2013 11:22:22 -0700 (PDT), wrote:

Does what I have described sound like a good plan? Can you think of
anything I could change that would make the shelf easier to make, or
less expensive? Thank you in advance for any help.

Purpose of "shelf"? What kind of load do you expect, and what dimensions?
Sounds more like you're building a bench...

I'd build the basic frame on a flat floor to make sure the frame ends up being flat. Don't use drywall screws, they're brittle and will snap under load.
Consider bracing the lower portion of the legs to prevent the legs from shifting/weakening under load. Or just use concrete block as another post suggested.

Unless I knew what's it for, it's hard to say.
A single shelf a foot off the floor? Why even attach it to the wall?
I'd call it a platform, because it's too low down to call it a
workbench. But maybe it is a bench, like for an audience.
If the floor is dry and is flat enough, one thing nobody mentioned is
what I'll just call "floor shelf."
Whatever color you want the shelf to be, just paint the floor that
color in whatever size shelf you want. So nobody misunderstands
your intent, paint or decal "SHELF" around the border.
The real beauty of the floor shelf is when something falls off the
shelf to the floor, it doesn't have far to go.