I had a 12x12 shed built last November for $1600. I had a steel subfloor used. Some shelves, windows, vents, pegboard, gutters, 30yr architectural shingles, etc added. I found a home builder that wanted some easy extra work.
It's the same quality, if not better, than a Tuffshed but came in for about 1/2 the price with all the upgrades.
My shed was partially built off site. The walls and trusses were done before getting to me. All they had to do was lay the subfloor then put the sides on. It took 2.5 days for the thing to be done. The shed was assembled in a day then the painting and extra stuff took up the other day and a half.
FYI, Home Depot contracts with Tuffshed. I went and talked to HD and they gave me Tuffshed's number. The HD models are pretty similar in specs to tuffshed's own line but there are some things left off to reduce cost.