[Al Skierkiewicz]

For what it is worth, rookies should take the kitbot chassis, assemble it without cutting for today and get it driving. You will find what works best and give yourselves some experience putting the parts together. But start driving. As you make decisions on what you want the robot to do, then start making parts. Please watch the Grant Imahara video on design. Unless you have a good veteran team helping you and have a lot of experienced mentors who might be able to bypass some of these design steps, you are letting time slip through your fingers.
If you have a welding shop capable of welding aluminum and if you have someone experienced enough to weld tubing, then 1" square tubing is a material that many teams use for the robot frame. It does require other specialties for robot building like knowing that square tubing will deform when bolts are passed through and hogged down tight.
Oh, one last item, the sizing box you need to fit into is unforgiving. You either fit inside or you go borrow a saws all and starting cutting. Plan your chassis 1/4"-1/2" under max dimension in every direction. (i.e. 27"x37"x59")