10mm buildings would definitely be closer to the footprint of an actual 6mm building. If you assume 6mm is pretty close to 1:300 scale, then 1mm on the model = 1 foot on the actual building. A Norman farmhouse might have a scale footprint of 40mm by 25 or 30mm and be 30mm tall.
Again, I can’t think of any commercially produced 10mm buildings that are designed to have playable interiors. The Warbases “mini hammer” 10mm line of laser cut kits are hollow, though. With a bit of additional effort you could make them with removable roofs. There are limited choices for building type and style, though. The attached picture shows a Warbases cottage next to some Baccus 6mm Roman civilians. Just my opinion, but the house looks a bit big (doors, windows especially). The footprint of the building is 35mm by 60mm.
I think it kind of comes down to what you’re trying to represent in the game. If house-to-house fighting is going to be a big part of the games, playable interiors definitely would be important (even if the interiors are very stylized and just represent areas within the building). If it’s mostly outdoors fighting, old work-around like allowing a base touching a building to “occupy” it might be the way to go.