Whoa, your wife married well
<applause>
Slab floor is great, I wouldn't do anything raised, just bed extra heavily in winter, a foot or more is not too much, pine shavings are *cheap* and you can pretty much just leave them there all winter or even longer. That will be plenty floor insulation.
Quonsets, and slab-floored buildings, and thus particularly slab-floored quonsets, tend to have condensation problems in the winter, esp. when you get a thaw-y spell. I would suggest making sure you have VERY AMPLE ventilation available for the building as a whole and for the coop area in particular, b/c you will sometimes really need it.
If you can insulate the part of the metal skin that the coop is against, it'd be a real good idea, not just in terms of temperature control but in terms of avoiding condensation and humidity problems.
You will probably find that if the building is left mostly-closed (with just some ventilation open) most of the time in the winter, it will likely stay significantly warmer in there on the coldest nights than if you had a small freestanding coop, so you have a big advantage there.
Be aware that chickens produce vast quantities of a fine greasy dust that gets on, and sticks to, EVERYTHING. If you have machinery, tools, vehicles, or anything else you don't want blanketed in chicken dust stored in the quonset building, I would strongly suggest solid walls on the coop portion (with ventilation openings) to minimize the spread of the dust.
BTW that is an excellent size for a coop and run, it would make half a dozen chickens VERY happy but has room to add a considerable number more if your wife prefers. Do not let anyone tell you that it is "too large" for a cold-winter area -- there is no such thing, if you want to concentrate the chickens' body heat around them at night you can build a sort of 'coop within a coop' enclosure around the roost so that they get the best of both worlds.
Good luck, have fun,
Pat