@a4arch, Yes but specifically some guys called Kenya Cast Products They say a pit that they make which is 3 meters cubed can serve 35 people and never fill up?

This is where by the house is friendly to the environment. like using natural light instead of electricity, recycling of water. using of solar energy to light up and using local available materials for construction. And many more. Expensive to build but very nice place to live in

I'm actually asking whether you have knowledge or know someone locally who can advice on this...

@nostoppingthis, yes i have. The info is usually given out as architectural drawings within the process of design as opposed to as a write up/advisory/discussion. Other architects such as Prof. Alfred Omenya of UoN can also give the same in detail. What @africancoloner said above is a description of the main points that will help shape up the final drawings in line with green architecture.

@african coloner, for low and middle class finished houses, the shell, including roof, is around 50 to 60% of the total cost. For high class finished houses, the shell is much lower, say 30% of the total cost depending on the cost of finishes.