Brand,
As designed, generally the edge of the foam shows on multiple story (armoury) kits. Either use black foam or use a black sharpy and disguise it.

On the hollywood flats style there is a roof edger that covers the foam and allows for a removable roof as well.

Several of us have done other things, really depends on the look you want.

Inset the foam hiding it behind the walls works well, but takes a bit more effort. Insetting the corner supports the thickness of the foam and all.

Bashing out a strip of print and edging the foam works also.