Many Nigerians errorneously believes that plan gotten from Europe or America will be  better than what the Nigerian Architect will give you.
There are a lot of reasons not to consider importing one ,some of them are

1)In tropical architecture due to high humidity, designs are done to expel as much heat as possible so that fresh and cool air will be absorbed, hence fenestrations or windows are of high priorities,but in western buildings heat is usually conserved therefore you may find less windows in some buildings.

2)The african man prefers showing off his house ,hence the aesthetic considerations is in the exterior of building while the western people prefers to have more of the aesthetic reflects in the interior of their buildings.

3)Religion also contributes a lot to the type of building your architect will design for you.

4)Culture is deep rooted in the African setting, can you say that of the western world?

5)Sociologically, you can't compare the two worlds side by side and not see a wide difference.

6)Security, if you look at some houses in Europe, they are practically designed for outsiders to view the interior of the buildings , very low walls or no walls at all are used, but what we have here tries to discourage robbers vandalizing our houses.

7)The big gap in technology also makes a lot of difference in the two worlds designs.

Cost: It is far more expensive to build a good house in Nigeria/Africa to the ones you have in Europe e.t.c

9)Economy: The economy of the countries that constitutes the tropical regions does not give rooms for too much of luxuries.

10)Erratic power supply.

11)Government incentives or Subsidies.

12)Development of traditional styles of building in africa.

13)Lack of maintenance culture.

Read full article      http://www.buildingcontractorsecrets.com/2008/06/western-architecture-versus-tropical.html#links