I sell metal buildings to contractors and individuals for a metal building manufacturer. I've sold them for the last 12 years, anything from backyard shops to big commercial and warehouse buildings to everything in between. Be careful dealing with the internet companies and building brokers, those you hear advertised on the radio and see advertised in the back of magazines. They will shoot you a low price but it is never the correct building code or wind loading for your area. Also the prices they advertise are strictly FOB at the plant, where ever that may be. Check out the MBMA website (
http://www.mbma.com/) and use one of the companies listed there. They are audited yearly in every facet of design and manufacturing and have standards to uphold.
Do not try to pour your own concrete or erect the building if you purchase one. In most areas of the state you are required to permit these buildings and don't let anyone tell you differently. Spend the money getting the slab correct to begin with and do not skimp on this. The two worst things I hear when I sell these to individuals are, "I have a buddy that owes me a favor and is going to do the slab for me one week-end" or "I'm doing it myself". I can just about guarantee you the slab will be out of square and there is nothing that will screw your erector up more than a messed up slab. These buildings are made to be plumb and square to bolt together. There is no slack in the buildings to cover out of square. You start talking about field modification then (cutting and welding to cover the screw-ups).
Erecting the building takes specialized tools to do correctly and also experience reading erection drawings and knowing how components are piece marked. You also need heavy equipment to unload and handle the components. The building is steel and nothing is light like on a wooden structure.
After a building is up, then a do-it-yourselfer can finish out the interior any way he wants. You basically have to frame all the walls up where you want them and put whatever electrical and finishes you desire. Note that if you put any plumbing in you have to do this before the slab is poured, needing some kind of plumbing know how.
In short, stick to a reputable manufacturer, pay attention to the concrete and erection, and you definitely can finish the inside like you want if your skills are up to the challenge.
One last note, the value in these buildings are in the 30' x 40' x 12' and 40' X 50' X 12' sizes for home use. 20' wide buildings are expensive for what you get.
Send me a PM for any additional way I can help you.