If by "main frame" you are referring to the structure that you will attache wheels, motors, and gearboxes to then I heavily recommend that you NOT build that out of T Channel as a rookie team. If you have students / mentors with tons of experience building their own FIRST sized robot chassis then you could be successful, but even then, I would say that you should just use the KOP chassis and focus your efforts on building super structures and game piece manipulators.
The KOP chassis is just so simply to put together, and of perfectly fine quality, that redesigning it isn't going to gain you much as a first year team.
Here is the page for the chassis if you are interested. If you are budget constrained, I recommend you spend that limited budget areas other than the chassis.