Karen properties are houses and cottages more often than apartments. Confirm the water source, most Karen compounds run on borehole, and whether the rent includes garden maintenance, which is standard on larger plots.
For this audience the single most important specification is a garden. Private garden space is the defining feature of Nairobi's low-density suburbs and the main reason families accept a longer commute from Karen, Runda or Loresho. It also carries obligations: at this altitude and rainfall, grass grows fast, and someone has to cut it.