I often find homes built on hillsides as a home inspector in St Louis County and St Charles, MO. Controlling and / or diverting storm water runoff is very important on this type of property.
Perhaps the hill is driving rain towards to the the overhead garage door, down a driveway. Sometimes a drain is installed in a low spot just before the door. These drains are, however, prone to leaf and other debris coverage, pooling, and diversion of the storm water directly to the garage.
Negative grade is common along foundation walls, where storm water prefers to sit and settle near the home, further away in the yard. Drain tile can help, and of course adding dirt along the foundation, to create a downhill slope away from the home.
I often see landscaping retaining walls, mostly for cosmetic appeal, catching and trapping storm water runoff against the foundation as well.
Any water trapped in / between soil and the foundation can wreak havoc on the wall, especially through freeze thaw cycles, which can literally push the wall in, creating new cracks and leaks.
Occasionally, downspouts are attached to damaged buried piping, and actually concentrate roof water directly to the spot you least want it.
Sump pump extensions are worth mentioning here as well, as I have regularly seen pumps discharging so close to the foundation, it creates a circulating pump cycle, pumping the same water from under the home, to next to the home, and back to the pump pit, time and again. While hillside homes are common, knowledge of how to best manage the storm water run off is not. It's a good idea to ensure that it's at least in the thought process while home shopping, and / or landscaping.
Kevin Dickherber Home Inspector St Louis and St Charles, MO