Bridget -
Another thing worth keeping an eye on when considering properties is snow loads on roofs.
In my county, snow loads are specified at 80 pounds per square foot (before any modifiers). But the adjacent county - and I'm within perhaps 5 miles of the county line, as the crow flies - is specified at 100 pounds per square foot. I think they're even higher near The Soo. (For those in metric land, this is about 360 kilograms per square meter and 450 kilograms per square meter - assuming I did the conversion correctly).
These aren't Lake Tahoe, Mount Hood or other western ski area snow loads, but for east of the Mississippi, they're non-trivial. Keep the local roof loads in mind when constructing outbuildings, sheds and barns and frame accordingly. I framed a 10-foot wide gambrel roof shed (for attic storage space) with 2X6 trusses, and don't regret it, though 2X4 probably would have been fine. But, I don't want to be on tenterhooks every time we get a storm, since it's at our lake property and I may not always be able to get out there pronto.
Metal roofs are quite popular, but they are not a panacea. If you don't install snow guards, the snow may slide off in places, at times, and in quantities that you do not want. Asphalt tabs (not very permie) - especially architectural grade shingles - will hold up pretty well. Cedar shakes on skip sheathing will last pretty well (as historic structures have proven) as long as there is good ventilation underneath so the shakes can dry out well. There is also historic precedent for slate roofs in these parts, mostly on churches, municipal buildings and the largest houses of the very wealthy, but I don't see much in the way of new slate roofs. The first cost will be high (even if you have the skills to install it yourself, that's likely to be true), so you'd need a long term view; over 100 or more years, a slate roof might actually be very economical, but you're paying for the long life up front. Not all buildings will have substantial enough framing for a slate roof, either. Even so, I do occasionally dream of Arvon slates...
Be careful about insulating vent spaces under the roof deck of heated structures. You'll want to preserve ventilation flow to prevent a hot roof deck, which will make ice. While it is possible to insulate sufficiently in this climate to prevent a hot roof deck, it is difficult to do on existing buildings. I could check the Army Corps of Engineers report from Fort Drum (I'll try to find the link and post it here), but it seems to me it requires something like R60, and it can be difficult to find enough room for that much insulation in an existing structure without major reno. Many older houses have been renovated in the last few decades to convert what was formerly unheated attic into occupied space (typically, more kid bedrooms). If done well, that can be fine. If someone insulated between the rafters right against the roof deck, and didn't build a vented double roof when they did it, it will be no end of heartache until you can add some venting - ice dams galore will ensue. Even 3/4" or 1" of vent space will make all the difference.
Fewer roof valleys will be better. Snow will tend to wedge into valleys, rather than slide down. But, my roof has 4 valleys and a shed dormer - it is what it is. Shed extensions with flatter pitch than the roof above may also hang up snow which slides down from above.
Broad eave flashing on shingled roofs cant hurt, though I've seen plenty of roofs without eave flashing which were fine, too. Sometimes, broad eave flashing signifies that someone was trying to compensate for a hot roof deck that made ice dams, but sometimes it just means that someone believed in overkill.
One way of dealing with heavy snow accumulations on a roof is to shovel (or scoop - the aforementioned Garant scoops are a lot nicer to drag up an extension ladder onto a commercial flat roof) the roof off two or three times each winter. There are also roof rakes, which can - at least theoretically - be used to remove snow from a roof while standing on the ground. I've seen, and used, multiple designs, but the pick of the litter, in my opinion, is the Avalanche brand. I believe these are Canadian, but I don't remember for certain. I have the 750 model, which is a bit sturdier than the base 500 model. I've still had to mend mine here and there, but they do work better than most, and are reasonably durable. Whatever the case, don't worry about getting the roof down to bare shingles; that's just a recipe for a torn up roof. Aim to leave a few inches of snow and just focus on getting the worst of the weight off the roof.
Keep in mind typical snow depths on your roof when installing vents and chimneys. If the penetrations are on the downwind side of a ridge, the snow can pile in deeply and cover up a sanitary vent. Even a clothes dryer vent should exit well above ground level (4 or 5 feet up isn't crazy). Direct vent gas appliances, as well.
If I think of any additional helpful hints, I'll add them to this thread, as well as the Army Corps report on insulation and ventilation of roof decks. It's a gem!
