You can make frame rails out some sort of c-channel metal. That would be most realistic. You can make them straight frame rails, or you can cut them and angle them, so they have bends in them. If you can weld aluminum, I'd use aluminum channel. Otherwise, stick to steel, which is easier to weld back up. Some guys heat the channel and then bend or form it, rather then cut and weld it back together. If you want it to be a really easy project, buy some Axial SCX10/Honcho frame rails.
http://www3.towerhobbies.com/cgi-bin...&I=LXXGD7&P=ML Or this -
http://www3.towerhobbies.com/cgi-bin...?&I=LXYYM8&P=7
If you want it even easier yet, buy the whole truck kit, and swap the body out for something you like better! Even if you want to scratchbuild the entire chassis, for a first time, I'd recommend you get the kit. It's got everything you need in it, and it's really nice chassis. Many builders like starting with Axial's chassis and components because they are really scale, perform awesome, and all the hard work has been done for you that way.