Map suburban house as a residential area?

Hi XavierTO -- my recommendation would be to simply put address tags on the main house, rather than worrying about tagging the land itself or the outbuildings. It's usually pretty easy to tell visually from the map which outbuildings are associated with which structures.

That said, there's no technical problem that I know of with drawing an area that contains the buildings in question and tagging that area with the address.

No technical problem... but there still may be reasons not to. It's almost always the house itself that is physically decorated with the address in the real world. When you decide that the address belongs to the whole lot, you're making an assumption -- a pretty safe one, but the real world is messy and before long you'll probably run into some iffy cases. A shared garage, an empty lot that may or may not belong to the house next to it, etc.

For ongoing maintenance of the map, it's better to have things tagged in a consistent way rather than in a surprising way. Most mappers will expect to see the address tags on the main houses, and might not even notice them on the areas, which can lead to double-tagging.

Another reason is third-party software compatibility -- many programs that use OSM data are written to expect addresses on buildings and nodes, and may not even recognize different schemes.

In short, simply tagging the main house is 1) good enough 2) much easier than creating an area or a relation 3) less likely to introduce errors of assumption, 4) easier to maintain, and 5) more likely to be compatible with software.