Reflector, it is really probably best to just get a stock one that has been proven effective. Trying to DIY that part really isn't worth the small savings plus you really want to maximize the amount of light the reaches the tank.
IMO: You better off focusing the effort on the hood design and just buy the reflector portion. If it's not a very wide tank, the PFO parallel reflectors are proabably the better choice plus it has place for supplement flourescents built in. If this is a wide tank, building around a lumenarc would be good.
What my ideal system would be 2x 250W single end MH and 2 36" VHO actinics. This is for my 65 gallon and I already have the VHO's, so I was going to make a 38" long hood/reflector that would fit everything underneith it. External appearance is not that important because it will be behind a wall.
PFO makes a parallel reflector is 36" long and should accommidate your needs just fine and can mount 2 MH in the reflector along with your flourescent supplements. This will probably focus more light into your tank than you can with a DIY. IMO: Relfectors is just not something to DIY.
If its inwall then no hood necessary just use cable or chains to hang the reflector....
Dirk should carry these along with most mail order places:
Great.....glad I was able to help. I was kind of thinking that you just didn't know what the options were out there without trying to DIY one and doubtful you could build to equal it in performance without some CAD and computer simulation type work involved.