Sourdough, I can say this. My cousin bought one of those pre fabs and it does look good, although it has been laying on the ground now for about 2 years! I guess that he seen all of the hardware and everything else, it just scared him. But, in my mind if you get a crane in there and a couple of helpers, it wouldnt be that bad of a job.
Hope I helped,
Chris

Pre-fabs are great if you are looking for a plain old shop in what ever size you want. However, if you are wanting to put jibs, hoists, or any ort of gantry system in they really dont cut the mustard. Most metal building companies will let you give them the demensions and whatever crane or hoist options for what they call a weld-up assembly. They can give you all of the stuff you need and most of the time will ship it right to your jobsite. Now if all you need is roof and walls the prefab is really simple and assembles fast. Weld-ups are cheaper in the actual cost of the building but take more time to assemble but you get exaclty what you want without having to do any rework or reenforcement.

Where are you located,I would not recommend the pre fab buildings if you can weld and have the time i would locate an outfitt and order your own beams and buy your perlins and pannels from them the other thing is the concrete i would at least have an eight inch slab with rebar and good wire mesh with good footers so if you plull in heavy equip or material you wont fracture the slab.the pre fab buildings to me are cookie cutters unless you can find one that has options that will suit you such as over head reinforced beams for hoist ect....also make sure insulation is included just my 2 cents

I have been working out of a prefab quonset hut style building for the past four months.  I like the reflective quality of the galvanized metal, it makes it easier to light the shop.  However, I am in West Virginia and we had a very mild winter in December.  Then January came and it got cold.  Even with  150,000 btu heater i could not keep the shop warm.  This is with an outside air temperature of 25 degrees on a cloudy day.  I contacted the manufacturer of the building for insulation options.  They sell a metallic faced roll of insulation 4' by 125' for $400 delivered.  It is applied using liquid nails type adhesive.  It sounded like a ripoff to me, so i got to thinking.  On the interior of the building, there is about 3/8" of thread exposed.  It was enough to fasten to.  I got some old 1/8" 6010 that had gotten wet and welded a rod to a nut i had made from some 1/2" round stock I had laying around.  Then I cut some lockwashers from old tin cans and drilled holes to hold the insulation on to the rods.  This arrangement is much  like "sticky nails" used to hold protection board on waterproofing material.  I made enough of these fasteners (110) to cover the section of the building I use.  I found some 6' by 24' vinyl faced rolls of insulation from a local source for ten bucks per roll.  This weekend i am going to rent the scaffolding and install it.  It was a lot of time, but so far I have 30 bucks invested.  So the moral of the story is,  Out there in cold Wyoming, you need some pretty hefty insulation on those metal buildings.

If you head west from where you are at towards GJ and look to your left down near the Parachute area you will see a covey of precast concrete buildings in a little industrial park.  Stop in and talk to the precast guy there.  He is making and selling waffle crete pre-cast panels there that you can erect with just a reach lift.  Will sell you just the panels you need and he has a neat precast foundation system too!  I calculated it it out an found that I was way ahead of the game over the COMPLETE cost of pre-engineered metal building. Best part is he will work with you and you can continue to keep adding panels on the increase the length of building as our finances and needs change.  The panels are easily insulated in the void portion of the waffle crete panel.  The thermal mass of the concrete panel goes a long way to reducing your heating bill in the winter.
If you must go metal building route, then contact the guys at C&O Buildings in Utah.  We worked to put a couple of these up for the Dalbo water hauling people in Rifle, CO a couple of years ago and these buildings went up without a hitch.  Not so for most of the other junk I spend a good precentage of my time fixing the red iron on.  Insulation is the key to a metal building and the crap that they sell you that you put between the panels and the wall girts and roof purlins does not come anywhere close to having the building spray foamed after you erect the thing.  Did a another 5000 sq ft one about a month ago and foamed it for about $6000.00 which worked out to be $11,000.00 less than the insulation package as supplied form the building manufacturer.  Thing is nice and quiet inside and does not resonate as most of these buildings do.  Additionally, the exterior metal panels now attach directly to wall girts and this speeds erection tremendously.  If you can get by the Dalbo facility up Mamm Creek stop by and look at the buildings.  They are a nice bunch of guys and were really proud of their new truck manitenance facility when it was complete.  Bag for the buck though; I would opt for the precast panel deal as you could have foundation (precast) in, wall panels erected and flying trusses in a long weekend with a reach lift and backhoe.
Good Luck!

Word on the street says that the building (Qonset hut) where the new elementary school in Silt, CO is to be removed and the guy that got it wants to sell it in sections.  He alledgedly is doing sme work for Prince Creek Construction.  apparently the building is plus of 150 ft long and as a quonset style could be divided and re-erected in sections.  Downside is adding on to it later.  But if bucks are a problem then check it out.  Unfortunately this is all I know cause I avoid Prince Creek Construction like a bad case of Malaria so that I don't get any on me.  If you know what I mean!!! 
One more of the thoughts about a building!!  Friends of mine bought one of those kit quonset buildings as advertised in the magazines like Popular Mehcanics.  The Mrs. of the deal beat the sales guy up good and got a 20 by 60 buildings for about $5000.00.  I erected it for them on their goofy thickened pad footing.  Went up easy but no end walls.  All total they had about $9000.00 in the dealincluding stick framed end walls and roll up doors (home depot close out) on each end.  Really sucks to work in though as the weld smoke seems to eddy in the rippled profile of the wall sections.  Takes a big fan to clear the place and the insulation.... well thats another story.  But if you just need a temporary deal for a couple of years or so then this might be an option.  If storage of vehicles or materials is the deal then this is a good choice for sure.  Got to plant some trees of vegetation around it to dampen the glare off the galvanized panels in the late summer.  No the experiment in painting it did not go well.  Just some options and I hope this helps.