I had a 14'x17' shed erected in half a day by Kelly Sheds.
http://www.gardensheds.ie/4-concrete-buildings
As long as you have a concrete base (or they can do this for you).
They arrive in the truck, go at it, hop back on the truck and are gone. Result, a perfect concrete shed, dashed outside.
I think the cost was €5k, about 3 years ago.
The shed is great. It consists of 6'x2' pre-dashed concrete panels that are bolted together, and a corrugated onduline roof.
Much cheaper than building one myself, and better than a metal or wooden one imho.
The only things I had to do was seal the base, where the panels meet the floor. If I had put in a lip around the base when I was having it pored, I would not have had do to this. And put in guttering.