I always wanted to have a stand-up desk for my home office so I would get a break from sitting at the regular desk all day. But gee, have you seen the price tag of a regular stand-up?
So I simply took a 4×2 and a 5×1 Expedit, topped with a Lack table plate. All this is held together by 3M Velcro Tape. Works perfectly, although I have to admit that smaller persons might need an elevation to stand on (I am 190cm/6ft3″ tall).