Funny you should say that as I was just looking at steel prices. I'm favouring aluminium because it's flatter and I may at some point move over to profiled rails. I saw a discussion on self levelling epoxy earlier today which I've put to one side for later (got to get some work done today), that could be a solution.

Btw, for me it all started about four months ago....
Oh you should think yourself lucky I reckon it start about 12 years ago for me. I've just kept putting it off and putting it off till I have a good workshop etc etc. I've still not got a good workshop space but I'm going to do it anyway. I have to admit though that I respect you for giving it a go in the space you have available, that's what I call real dedication.