I've only been here for like an hour I have already seen a ton of threads with step by step instructions to making your own micro grow using a pc tower. Search.
Basically you need:
Lights
Soil
Container(s)
Seeds
Nutes
Timer
search for the PC case growers thread...it will answer all your q's
cover the inside with foil tape, start mounting your lights, fan(s), and stuff...get a timer...pots...
Computer fans are reasonable from 10.00-100.00 at radio shack, best buy. Not to sure where your from. I say start with your lights first, depending on what type and how many your using will depend on what size and type of axial fans you'll need. Next wire it all up. I took the material the use to make windshield sun covers, liquid adhesived it to the inside of my cabs. Just what I did.