Garden shed?

Well, the snow is coming. I've been out rounding up dog houses for all my pens of chickens. I've recruited my younger brother and we've driven all over picking up nice wood, weatherproof doghouses for the birds. I can't stand to see another winter where they have to huddle in plastic barrels. Not right. My dad is very big on the whole "just do enough to get by" and and then, classicly, nothing ever gets built, including the chicken coop I've been promised for years.
A wanted ad on craigslist has helped me get several FREE (i was willing to pay..but these people decided they didnt want them? One mans trash is another's treasure! I love craigslist.)
Today we dragged a mammoth one into the pen for the canadian geese. It's snowing and sleeting outside right now, but there in there nice and dry now
My sister's horse is standing in the cold, and doesn't have a blanket yet. If they wont get him one, I will buy one myself. "We're going to get a barn built" yeah...in about...10 years, after I'm long gone and the horses are dead or sold. Haha.
Anyways, I get off topic. I want to get a horse, but I couldn't stand to see her sit in the cold all winter without some shelter. I was thinking...Would a garden shed work for a one stall horse winter shelter? Even with the wood floor? Has anyone used a shed for a horse barn? I could find one on craigslist.
Opinions?