Being a poor college student I also looked into a do it your self roof rack. This is what i gather.
Atlantic British sells the roof mounts for a RRC $50 for 4 and D1's and 2's for $80 for 4.
If your planning to put anything substantial you'll need 8 mounts. I read somewhere that the drip rails are only rated for 160lbs factory rating. I know people are putting more, but with that in mind weight is the critical issue for anumber of reasons.
It will determine how much you can load it, will help to keep your CG down, and make it easier to take on and off.
Use of aluminum is necessary, i bought part of the steel to do mine and realized it was going to be way too heavy. So you need access to a Tig welder.
Rounded corners, you need access to a tubing bender, like 1" .120 wall to do the perimeter and 1x2 .120 wall rectangular tube for the uprights and across the roof.
Im planning in customizin my rack to have purpose built holders for various things, shovel, jerry cans, spare, etc. So make sure to spacial reference that all out. Keep in mind fluids are heavy so is a large tire and wheel.
A wind deflector seems to be a good idea, my friends roof bike rack minus the wind guard howls horrible but is bearable with the wind deflector.
thats about it i may sit down and do the math to see what yielding strength is over the with of the vehicle with a point load in the center. but other than that its pretty much up to ou and what you want to use it for.
91 RRC Hunter Edition "The Warthog"
Made a bunch of stuff fer it.