Well i've been looking into roll bar legality and whatnot for our little project.  quick summary is its going to cost us, auto-x rules are easy and everything else isnt (require full cages and $$$$).  i checked one place online that gave me 20ft of 1.75" .095wall DOM tubing for 85 bucks (you dont want to know the shipping, hehe) we can contact local companies when its time

Assuming we probably wont do much more that autox and some HPDE track events this shouldnt be a big deal. 

Autox rules are vague so i went up a step to the scca ProRacing regulations to get info on stuff like tubing sizes and whatnot. 

Mounting Plates

-no less than .080" thick

-Max area of 144 sq. in. (couldnt find a min area)

-plates may be multi dimensional

Material

-seamless or DOM, mild steel

-no ERW tubing

-3/16" inspection hole in non-critical area required

-gussets recommended at all joints

-radius of all bends must be no less than 3x the diameter of the tubing

-all tubing subject to driver contact must be padded

heres the info i found on tubing size. turns out we should only need 1.75" .095 wall tubing

weight measured as raced minus driver and fuel

Main Hoop

-Must be full width and continuous

-must have smooth bends with no signs of walls collapsing

-must remain in one plane

-be as cloe to the roof as possible

-must have a diagonal to prevent lateral distortion

Rear Braces

-Must be attached to the main hoop not more than 6" from top of hoop

-must make at least 30deg angle

notes:

Definitions of DOM tubing on the Web:

• Drawn Over Mandrel. Formed from strips and electric-resistance welded, then cold drawn to size. The cold drawing process causes the weld line to virtually disappear and gives the tubing it strength by cold working and allows consistent dimensions and tolerance. The carbon content also gives DOM (1020 or 1026) better mechanical properties than regular ERW tubing.
  www.desertrides.com/reference/terms.php