Two kinds of unit: ones you own, and ones a leaseholder owns.
A building needs its units — the flats inside it. Add them once the building exists.
On the building's Overview, select Add units.
Each unit is one of two things, and the dialog has a tab for each. One of my properties is a flat you let, on your own compliance — pick it from your existing properties with Add, or type a new address and Add property.
A leaseholder's flat is theirs, carrying its own service charge, ground rent and compliance. Which tab you choose sets how the flat is treated from then on.
A leaseholder unit's service charge and ground rent are tracked on the building's Service charge and Finance tabs, and on that leaseholder's own Statement.
