Here's some ideas from a closet we built.
(Click on a picture to enlarge it)
We used 3/4 inch MDF board only. We cut it down for bracing, trim, shelves...pretty much everything except the hanging rods was made out of MDF board.
The biggest challenge was extremely small closet space. We had to get creative to make everything fit. (Plus there was a designer working on this job, that's where the "creative" came in!)
Instead of over-cramming stuff, I built a box in the corner and left it empty, dead space. We only lost that 12" x 12" very hard to reach corner.
We took over the garage for a couple days and used it as a shop...
Here is a finished view before the painters came in...
The shelves on the left are for normal shoes and high-heels. In the top picture, you can see the shelves on the right that were spaced differently for taller shoes and boots.
The open spaces in the middle are for various length hanging clothes.
The man's side was similar, but all shelves were custom placed so you could use them from everything from tennis shoes to boots to work boots.
We like to visit Ikea and other large home improvement and furniture stores to get ideas on different styles. It's so much better to see it in person and see what works BEFORE you pay someone to build it!
We have even had a client that had cut-out cardboard so they could visualize the size of the shelves better! A great idea!
Happy Closet Building!