You may have to do a false roof not just above the staircase void but the entire first floor slab. The reason being a concrete slab is permeable so you should otherwise expect water leakage through the slab. Doing a maisonette in phases can be quite expensive.

A better mode of construction would entail doing the entire first floor walling including the roof. The finishes on first floor can follow later as you chill on the ground floor.

Excellent observation my sister. But shida ni pesa. I don't have enough to even fika the ring beam let alone the roof!
I was thinking just build a mini mabati roof over the staircase area and then move in. I never knew concrete slabs are permeable? Aren't some roof tiles also made of concrete? I would think a think suspended slab is virtually impermeable, and the water that seeps in and is retained is actually good for long term curing of the slab? Asanteni for the feedback.

There is no aspect of construction which is cheaper than doing masonry walling. If you do not have cash in the interim to lay roof tiles, you may roof with gauge 32 mabatis which shall double up as underlays for the tiles at a later date when your financial position improves.

Queen yes I agree with you on walling but you forgot the small matter of roofing mbaos and roofing labour! Hizi mbili sio mchezo. Ring beam pia will eat money.

I lived in a house with slab roof for 4 years with zero leakage.just ensure no water stagnates on the slab