Just found this nifty little app which lets you quickly create 3D spaces for FREE!
You can drag walls to the measurements you want, and refine those measurements by taping on them, add windows, doors, internal walls and furniture. Decorate the floors and walls and even put yourself inside the room to look around.
You can create custom room sizes or start from a template and add multiple floors. Great for just quickly visualising something in a 3D space.
You can see the full project here or search Amikasa on the app store.