[AtomicLabMonkey]

As said, the frame would be heavy using steel. You'd have to go with pretty thin wall tubing to mitigate the weight. Alum is much lighter but will cost a lot more; it's more difficult/takes longer to weld and the tubing cost is higher than steel. It's also not as rigid as steel.

The design as drawn is pretty bulky; you might want to consider bolt-together sections, like a separate front & rear clip that bolts together or is hinged for fold-up, and uprights that will come off the base frame - to make storage a lot easier.