Have someone do the concrete for you, and then setup the building which is the easiest part. Concrete is expensive, requires skill and the right tools to do a good job on a large slab quickly and efficiently. A power trowel and power screed can be rented, but the screed especially takes a lot of skill to do a good job and get it level and flat quickly and efficiently.
And it really helps to have a laser level also. Otherwise you need some method of determining when the concrete is at the right height, which is hard to do if you want to get a large slab of 30+ yards all poured quickly, and have it setup at the same time so that you can use the power trowel on the entire floor at one shot.
The building is just bolt together, and follow the instructions that come with the kit. Generally you bolt a set of collumns and the rafter together while it is laying flat on the concrete, and then set it up over the bolts. You set up and plumb at least two interior columns, if your building is large enough for that, and then work you way to the ends as these rafters are much smaller due to having end wall columns to help support them.
The key is having the bolts in the correct locations in the foundation, and having the foundation level and square so the building comes together properly. After this it is just bolt and screw together.
Usually, these building also are insulated at the same time which makes installing the steel a little more difficult and time consuming, but it really isn't that hard if you have several people to help you.
Putting up a building like this definitely isn't a one man job!
By the way, rebar is pretty expensive, at least it was back in 2004! I poured a 20'x65' apron on my shop that fall, and the rebar was 1/4 the cost of the concrete, which I poured 6" thick. And I only put it in on 3' squares, not 2' like some people say you should. I did this all myself by hand, with only 1 helper, including hand troweling it, which about killed us! Next time I am renting a power trowel! And I poured 1/2 one day and the other half 2-3 days later.
But only it cost me about 1/2 of what it would have if I would have hired it done. This didn't need to be flat, so I wasn't afraid to tackle it. It slopes down 6" in 20', so any minor low or high spots aren't apparant because at at that slope water never ponds anywhere on it.