Go to wescottsauto.com they have the blueprints ya need for free...
I built my 31 A chassis out of 2x4 and 2x3
.120 wall rectangular using wescotts plans, came out very nice.. Got the metal from the local steel yard 24 feet of 2x4 was around $65 ??
and 12 feet of 2x3 was around $40 only other thing I had to buy was the stamped cross member at $79 and a couple weekends of work, looks as good as anything you can buy