Make sure to CAD and model the entire rolling chassis. Explode your assembly and make sure your fabricator can make all the bends. You will not be able to bend 6016 T6 use the 5052. We typically use .080 for most of the parts and carefully use some .125 for strength. Keep your total number of individual parts as few as possible. All of your fastener locations and fastener choices should be pre engineered. Don't go crazy and cheese out to much, this is your foundation, but keep close track of weight. Understand that fabricating dimensional tolerances are not as tight as machining tolerances, you won't be able to bend to +- .010. It is important that your assembly is square and stays that way. Planning and drawing are important, much can go bad very fast. We have built several fabricated chassis, each one better than the last.