I believe that you can use the Box on the miscellaneous to make a platform then just change the texture of the box to your liking. now the house floor and the subfloor wont be at the same level, you can just make the wall a bit higher and just add the same box just wider on the floor and just elevate your furniture and doors and windows a bit and you should get what i belive is a subfloor
This is what i did:
its a very simple house just to show what it isThis is to show that the floor inside is the same level as the outside one:
you said that it doesnt have the same perimeter as the real floor:
P.S i did the subfloor on the outside so i can show it you can do it inside as well,more professionally, (Your house probably looks a lot better)
I hope i could help with this one
