When I hit "control" it still doesn't give me an "add level" option. Only choices are "modify compass" and "import background"
As for my 10 year old computer not supporting SweetHome3D... I had a mac update and needed to add an application I needed for my business. The only way I could get enough space on my computer was to remove anything none essential. I'm missing it so much though that I may have to make some changes (like maybe a new laptop lol)