What tools do you have? (or what techniques are you already comfortable with?)
And what are the closet dimensions? (my first thought is to skip the returns on the ends, and to ask if you really want a lot of shelves and drawers in the middle? How will the space be used?)

One of the first projects I tackled was a closet organizer design from Family Handyman, except I kept trying to make it more complicated.
(I don't see the exact project, but they have a decent article on closet organizers: )
I grabbed red oak plywood from one of the local borgs because I thought oak sounded cool and it wasn't too expensive.
I learned to really dislike this stuff -- when I encountered voids (the outer veneer would cave in because of a gap underneath), or places where the glue laminations failed, or where the pieces bowed when cut -- this was especially annoying when trying to make drawers. I also decided that I didn't really like edge banding. This was finished with general finishes wipe-on gel varnish. I decided that I did like that finish method.

My second organizer was much simpler. For a 6' span, I had a top shelf near the top of the closet, then 2-level rods across 4' of span, and a tower with 2' of long hanging and then an intermediate shelf with some space below the top shelf. This used a sheet of birch plywood with solid edging. Finish was a light coat of watco danish oil (don't let this get too thick, and it will need some time to dry out). Overall, I preferred this simpler design and build.

If you can get old plywood on craigslist, that can be very stable and much better (for the price) than what you can buy retail. If you paint, don't use paint designed for house walls -- it ends up very gummy. (this was a mistake I made on a rehabilitated corner hutch)

Good luck!

Matt