I've been retired for a while, so am not as current with regulations as I used to be. But generally speaking a structure in Calgary under 107 square feet does not require a permit, foundation or not. There are exceptions, such as a structure attached to a house, tent garages, and most municipalities don't allow you to "no-pool" your outbuildings (Calgary included). This means you can't get around the square foot rule by having two or more separate out-buildings that collectively exceed the 107 square foot rule for the given lot size. It would be in the Community Standards Bylaw, Land Use Bylaw or zoning restrictions (permit required) to go past a specific percentage of your lot footage devoted to outbuildings. I think it used to be 20%, but again I'd have to double check...it might be lower. This caveat was added years ago specifically because people would try to get around the outbuilding cap by having multiple sheds—thinking the municipality wouldn't figure it out (they do).
There will also be restrictions in Calgary and other places related to set-backs from the street, utility ROWs (Rights of Way), as well as adjacent lot lines and even possible overland drainage (actually a big issue).
FYI, in municipalities with sophisticated GIS systems that do aerial surveys (like Calgary), they spatially correct the images they take and feed them into software that can analyse the footprint of your outbuildings and compare it to your lot size. Using this information they can verify assessments for tax purposes, and calculate whether or not your outbuildings, deck size, swimming pool, unidriveway, etc., exceed what is permitted for your given zoning. Based on this, the municipality can legally reassess your property or send out bylaw officials for specific violations. Outbuildings are one example.
They also have more sophisticated technology that can detect thermal anomalies such as grow ops. This, and other technology from the same pics was in fact used to find dead bodies outside of Calgary (Airdrie) in the infamous Douglas Garland murders several years ago. I recall seeing some thermal peaks in a residential image once no one could figure out. They were off the charts for the residential area and really baffled the analysts. It turned out to be a blacksmith forge in a backyard.
Unless the municipality is hard up for cash (and certainly not in an election year), they don't do this kind of analysis routinely. But they will do it when there is a complaint. And generally speaking, they don't do it every year—often every second year (due to budgeting). So if in your example a complaint is lodged, the first thing The City will do is check the latest aerial survey and compare outbuilding size to lot size as a percentage. This is automated.
If you ever see people putting camo netting on their out-buildings or RVs in the fall, they are doing so because they understand
when municipalities do this aerial photography. I've seen examples of it when I still worked for government. It always occurs in the fall season because this is what is known as "leaf off" season—or the time of year when the leaves fall off the trees and the planes can photograph the buildings (and determine square footage) better. Using thermal imagery, a municipality can distinguish the thermal signature of an outbuilding from the primary residence.
In rural areas, townships generally don't have the money to do this kind of aerial photography as cities do. However, if you live in a township or place such as Airdrie that is just barely outside municipal limits you might get photographed—big cities usually fly over an "overlap" area that will include your town. This is how Douglas Garland was caught and the bodies were noticed—it was Calgary doing the flyover that took the pictures.
Having said all this, I have a recommendation for people that are upset because a neighbour possibly built/erected oversize outbuildings for storage, or they are welding or grinding in their garage, etc. Unless there is an environmental or safety hazard, or the violation has a big impact on you or your property (e.g., overland drainage), think seriously before reporting someone. A minor issue like having an outbuilding a few square feet over the limit can cause irreparable relationship damage in a neighbourhood far exceeding the small infraction itself. Often the issues can be resolved with a simple conversation between neighbours.
Sorry for the rant