The amount it will cost to construct a building depends on a number of factors which, typically, include location, the type of house one is interested in, the finishing, fittings, quality of the building materials, site geography, among other things.
Basic factor that one should take into consideration is the size (area) of space to be built on. The easiest way that one can estimate how much their building will cost is by consulting someone who has recently built a similar house in the area.
It is easy to find such a coincidence in housing projects since they are all similar in size, space provision and finishes.
BUT, best way to do a good estimate is consulting professionals(QS) like wakanyama & co, da vinci etc.
To get a rough figure of the cost, take the price of the home, deduct the price of the land and divide that amount by the size of the house (measured in square feet). it is advisable to use several recently built homes in the area that are similar to the one you wish to build to ensure that you get a fairly accurate estimate of the cost of construction.
The point here is that if a house is selling for Sh2 million while the price of land it is built on is Sh1 million, then the construction cost will be approximately Sh1 million.
However, for other types of buildings whose designs differ from those in the vicinity, the Institute of Quantity Surveyors of Kenya has developed guidelines for the major towns by picking recently completed projects, measuring their sizes in square metres and establishing their actual construction costs.