@DarkestPenguin Best way I found is using the up/ down arrows in the top panel next to where you chose the rooms height, the big arrow in the middle of the room only alters the height of the whole foundation.
so if you place a room using the build room tool, not wall tool, and use the two arrows it will move the floor within up and down not the whole build,then you can add another full room and tweak that one to be a different floor level than the one it's attached too. You might need to change the wall height of the main room to make it work.
This way you can remove all the walls on your patio build and keep the ceiling.
It helps to go to an empty lot and start a new build and play around with it, to get used to how it how it works. Newcrest is perfect for experimenting with builds.
Hope this helps 🙂