Check out http://www.inboardtalk.com/tower/tower.html
where Matt built his own. That got me started on what turned into Monster Tower.
Research the old posts here, many have built their own towers and some of the most innovative ideas I've every seen in any wakeboard tower came from guys that built them in thier own shops.
Shoot me an e-mail or give me a call if you go for it. I'm a major "do-it-yourselfer" as well and will be happy to help. I can probably point you in the right direction on some of the "parts is parts" that you may choose to use. Bill@MonsterTower.com