A rock-solid foundation
A small building doesn't require a massive foundation, but it does need to be strong enough to withstand the ground-heaving pressures of a Canadian winter. On-grade foundations are acceptable, but a pier-and-beam foundation is a better choice because it gets below the frost line with the least amount of excavation; it requires only that you dig holes for the concrete piers. Piers also allow a structure to rest on a slope or uneven ground. You have to build steps up to the cabin, but that's an acceptable sacrifice for a building that can withstand the forces of nature.
The location for my building is unique: the concrete-block piers rest on solid bedrock, each at different levels. The front corner of the cabin is almost flush with the surrounding grade, while a rear back corner sits on a pier that is 36" tall.
Uneven ground requires special attention. After excavating down to solid rock, I determined the location and height of the six piers using a six-foot spirit level resting on a straight length of lumber. I levelled the straightedge with one end resting on the highest foundation point and dropped a plumb line down to the bedrock.
When planning for poured footings, I made the distance from the beams to each footing divisible by the height of standard full- and half-size concrete blocks. Small discrepancies can be made up with mortar without having to cut concrete blocks.
I fit the poured concrete footings to the uneven bedrock with custom contoured forms. To build the forms, I made a plywood box the size of the footing and levelled it in place using short lengths of 1x2s spring-clamped to the form. A felt marker duct-taped to a scrap 1x2 served as a make-shift compass to scribe the contour of the underlying rock to the form. I scribed the entire perimeter of the form, then cut away the waste using a jigsaw. The resulting form fit the rock perfectly, so I repeated the steps for all the forms.
Before filling the forms with concrete, I added two 10" lengths of 1/2"-dia. rebar to each one. I drilled a couple of five-inch-deep holes in the rock using a rotary hammer with a masonry bit, then drove the rebar home with a small sledgehammer.
Next, I mixed the concrete and poured it into the forms, taking care not to shift them. I levelled the wet concrete to the tops of the forms by scraping off the excess with a scrap of wood. Once the concrete cured, I stacked concrete blocks on the top of each pier with 1/2" of mortar between each block, using a level to plumb the corner blocks every step of the way.
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