In reply to jfryjfry :
As a professional contractor, I wouldn't do that with steel without an engineer's seal. I wouldn't be concerned if it was wood.
The problem is the dissimilar metals and the wind lift. You would have to secure the aluminum structure to the steel beam with a method that accounted for the wind lift. Probably a bracket welded to the steel and bolted to the aluminum. That's a lot harder to do well than bolting the aluminum to a wood beam.
And it would be much cheaper in wood.
The LSL/LVL beams come in 1-3/4 widths that you can join together to get wider beams, which make them scale up easier without a single huge heavy beam to deal with. I'd guess you could span 30ft with three of them (5.25 in) at 16 inch tall, and just two (3.5 in) at 22ft, maybe even just 14 inch tall.
You would need to do calculations to know exactly.
Let us say $500 each, you need four, so $2,000 in beams, then the columns to hold them up, some concrete work, and hardware, call it $3,000 in materials.
In reply to nimblemotorsports :
Everything you said is true. Some of it may be correct.
It's not good when you say things like "I guess you could span 30 feet", or "..maybe even..", or "..you would need to do the calculations to know exactly".
Span tables will show ability to clear span with a load and a particular deflection. They WILL NOT show anything about wind lift.
The load is fairly simple. The lift is not.
Did you say 18' span? I lost it in the comments when I saw.
Do not quote me, but I think that you are going to need to have at least (2) 2x10 on each side to support the roof on that span. *its been 7 years since I built and mathed the shop I built.* If you have the concrete, you should be able to bolt a "mount" to the floor and run a 4x6 or potentially 6x8 to hold the weight for the support.
You could cut down on height of the support by going with a steel piece. As SVrex says, it may be tougher to do, but you can potentially save size and weight if you go that route.
Again the issue is the lift, not the load. I could probably lift that structure at one of those column supports entirely by myself with no assistance. They are really light.
