I've been working with sketchup (http://sketchup.google.com) to design a custom wardroom with sliding doors. I found the tutorials "Start drawing Parts 1-3" very helpful http://goo.gl/COcjU. It allowed me to get up to speed fairly quickly. It also allowed me to work out exact dimensions. I'd normally draw an approximate pencil plan and eventually that would get made into reality.

I was using the homebase site catalog for sliding doors (http://goo.gl/fO9QQ) and maple wood (http://goo.gl/AI6C0/) dimensions to construct a basic model. The sketchup screenshot shows where I got to. Its basic, but this allowed me to quickly see that it was going to cost something like 500+ to build vs say something like ~352 for http://www.ikea.com/gb/en/catalog/products/S89894794#/S09875488/ from Ikea.

Admittedly my version takes full advantage of the ceiling height, I'd enjoy making it and it would probably fit a lot of clothes. The bed room height is 2.85m. This design is 2.4m (H) x 1.64m (W) x 0.66m (D) and fits between the wall and radiator.

Off the shelf will always be cheaper sadly, so I'll have to consider those over custom build :(