Long before you go looking for steel you want to look around at dealer lots not the new stuff the junk in the back, at auctions, look what people have fabricated, what they used, what seems to have worked. I do that all the time even if I have no plans to build something. Seeing a good idea, and then when you see a part, that was used, you might want to keep it rather than throw it out. I wish I would have kept, a few truck tie rod ends for use as base pivots.
You will also see things that did not work, that is the information that can save you a lot of time and money. Better to learn from others mistakes.
The Quality of everything you do depends on the amount of time you are going to use it. Spending thousands on something you use once is a loosing proposition, but scabbing something that will do the job from a junk pile that takes vision.
Just a thought!