you cannot make a ballist.... they run around $35 at an electrical store... each bulb needs a specific ballist.... unless you get a NMH/HPS conversion unit.... but I got my ballist, 400watt hps and my fixture for $90.... mind you I have a guy working at the store... and get the employee discount... my 100watt hps only cost me $5 for the bulb... never did get the ballist for it.... just went to the 400 watt... as to a housing... I used sheet alluminum, I got it from the local hardware store.. it was 36" tall and ran $5 a linear foot.... add on some support brackets and you got yourself a housing.... attached is mine.
the ballist and light that arn't on in there are just my back-ups,
incase my bulb fails.