See the breakdown below:

For a 4 bedroom flat

Foundation digging and bricklayer workmanship- #160000-#200000 (Depending on areas and the contractor)

list of building materials needed for foundation
(1) blocks 6 inches400 pcs @ rate of 300
300x400=#120,000
(2) blocks 9 inches 400pcs @ rate of 340
340x400=#136,000
(3) cement 20 bags@ rate of 4600
20x4600=#92000
(4) granite 10 tons =#120000
(5) sharp Sand 15 tons =#75000
Total balance #543,000

From Foundation to Lintel:
2000 blocks 6inches@#300=#600000
20 bags of cement@#4800=#96000
Bricklayer workmanship =#180000-#200000


Casting at Lintel level
Granite- still available
Sharp sand. 15 tonnes = #75000
Carpenter- #80000-#100000
Welder(Iron)+workmanship = #160000 (materials =#150000 and workmanship =10000)
10-12 bags of cement@#4800 =#48000
Bricklayer workmanship = #60000 or more

After Lintel casting there will be two levels of blocks for roofing level
600 blocks(6inches)- #180000
6 bags of cement-#30000
Hopefully you still have sharp sand left over
Workmanship- Negotiate


Water and Owo omo onile varies depending on location.

Other things
Tank or reservoir for water
Buying water or dig borehole for which you will need a generator to pump.

Thanks