I need a large enough reflector to disperse a 500w halogen evenly to flower my plants also do Yu think th's is a good idea
Halogen will not work. It puts out way too much heat for the light you get, and the spectrum of the light you do get isn't right. Making a reflector isn't that difficult, but you will need another light for it.
FTW is correct, you will have no end of shit with this kelvin unless you stick a blue Hollywood filter over it, even better get this: http://www.amazon.com/Apollo-Horticulture-Dimmable-Reflector-Accessories/dp/B004YXDHX6/ref=pd_sim_lg_68
Yup, like the others said, a halogen is completely the wrong lighting spectrum. It is the worst possible light to try to use for growing. Look around for a used HPS or something.