IMO, you're a lot better off using good reflective surfaces on your walls than trying to make a reflector. If you're really concerned about losing light in that way, just buy four 10" clamp lights (they come with a very good reflector) at Wal-Mart and put Y-sockets in. You can get about 13000-14000 lumens out of that type of setup, and it will run you less than $70 total. Ideally, you'd have another two lights hanging between plants for under canopy coverage. It makes a huge difference with CFLs.