Aerial map on google or wikimapia can give you some information pertaining your needs.
If you do not want flats build around you here are some options in my views.
1. Buy plot in an area where people have already settled = more expensive but assured of the type of houses around.
2. Buy away from center/highways. The map can guide you or even visit. Land here can be cheaper but hard to settle immediately.
Now for your preferred location (40km from Nrb CBD)+ a budget of 1.5m = along Thika rd, Kangundo rd, mombasa rd, Namanga rd. or Ongata sides.
3. What about the mixture of 1 & 2 above.
This link is exactly that:
http://wikimapia.org/#la...934292&z=19&m=b
This plot (1/8 acre) is on sale at 1.3m neg. About four or five maisonettes under construction, there is a school, a gated comm.. houses and... just see for ur self in the map. But note that this map was updated early 2013.