Also see: usage
Any other examples are welcome!
If you use the landuse=residential-on-buildings scheme, you can use Convex Hull to quickly draw the outer way:
Select the buildings and activate Convex Hull.

Alternatively you can use Shrinkwrap to fill in the holes on the NE-side.
Say you want create a way that's just a little different from an existing one. Just select the way and use Shrinkwrap to make a copy.
As an example I want to create way for the leisure=park within this tourism=museum, but that way needs to wrap around the main building.
Select the way I want to copy and activate Shrinkwrap.

Modify the new way to wrap around the building.

You could of course also solve this with multipolygons.
I already mapped all the buildings and walls enclosing this park.
To add the inner leisure=park way without having to press Ctrl+f a million times I can use Balloon.








