PS. I am in zone 7a. Central Maryland.

It's been my experience that an unheated shed or garage is better - the rose goes into dormancy and stays there. A slightly heated or variably heated space may 'confuse' it and make it start growing before it's time. I had a lovely rose (Color Magic) that I over-wintered for 2 years in my garage.

Hope that helps!

Here is a link that might be useful: The Stubborn Gardener

I overwinter mine in an unattached, unheated garage in zone 5b. I rarely have a casualty. I put the pots in styrofoam cones for insulation and put garbage bags around the pot and the lower part of the rose. I will pour some mulch or leaves around the bottom of the plant to help cover them. Seems to work well for me. I usually go in and give them some water once during a thaw so they dont dry out completely over winter. For miniatures I will group as many of them that will fit inside a cone and cover them with leaves........

Where you are, I'd put them next to the house foundation. Even a detached shed is going to be too warm, and they won't stay dormant.

I winter mine against the house. I build a wall with burlap and then pack them with leaves. 6 winters now and they seem to do very well that way. I do have one tree rose that goes into the shed because of the graft being up so high up. I wrap it with newspaper and burlap and put it into the shed. If you do put them in the shed or garage you need to do two things. 1. Put them up on wood blocks off the cement floor. 2. Water them a little once a month. Drying out can be deadly for them. And if you leave them outside pile snow on them when you shovel. It's good insulation and it also keeps them moist. We snow blow toward the roses so they get a good blanket all winter.

I concur with putting them next to the house and mounding leaves over the pots. Ideally you want to keep the temperature in the rootball between 22 and 40. Roots are more tender than canes because in nature they are protected by ground heat.

seil-- Consider that, while concrete feels cold to the touch, it is actually warmer than the nighttime air because of ground heat (except maybe next to the exterior wall). So the wooden blocks are probably not helping your pots.

OH NOOOOOOOOOO Way too soon for this discussion ) :

LOL. Yeah, really!

It isn't just for insulation, Michael. Cement is very porous and will draw moisture out of the pots.

Is one side of the house foundation better than another? Am I looking for the coldest side, or something else?

(Yes - it is early. I'm the opposite of a procrastinator - I like to know there's a plan "out there").

I'd say east is best--sheltered from the winter winds but not sunny enough to encourage premature growth.