Many homes are designed with the primary family living spaces at the back (kitchen, breakfast room, family room). These are the rooms you want sunlight in; the rooms with all the expensive windows.
And you'll get that sunlight through those windows, too - if the back of the house faces more or less south. That's where the sun is, remember?
If your lot is on the south side of the street, great.
But what if your lot is on the north side? All that living space, all that glass, isn't going to get any direct sunlight at all. Or worse, your lot faces east, and the afternoon sun pours through that wall of west-facing glass like a blast furnace - heating up the house and fading the furniture and carpeting.
Since we're talking about sunlight, now's a good time to bring up the subject of energy consumption. Houses are designed to keep heat in, or to keep heat out, depending on the season. The easiest and least expensive way to keep heat out of the house is with proper orientation of the windows and doors. The easiest way to keep heat in is to reduce the number of windows. So, pay close attention to the number and location of windows in your design.
A properly oriented plan can save you a lot in fuel bills and give you a lot more enjoyment of your house and your building site.
It's amazing, every time a backhoe starts a new house foundation, how different soils can vary from one building site to another. From loose sand to solid rock and everything in between, and sometimes all on the same site!
Soil type can have a big impact on the cost of construction. Even if you know a lot about the underground conditions on your site, it's a good idea to keep a little cash in reserve to deal with potential surprises lurking under the turf.