I think a4architect left out details on what the length of the boundary wall actually is in his calculations hapa which might be the reason why he is losing me in the mathematics on the cost of the boundary wall.

Correct me if I am wrong here; assuming I have a plot with a total perimeter length of approx 100m, foundation wall depth is 1m and height above ground is 2.5 m. Then my total cost for middle cost finishes would be

100 x 3.5 = 350 sqm
350sqm x 1200 shs = 420,000 kshs

Kweli/rongo?