How much do you know about the soils on your home site? It's relatively easy to learn the basic characteristics from your County Extension Service or local building department. You might also contact builders and excavators with experience in the area and ask them what they've encountered on other projects they've built near you.
Some types of foundation systems that are popular in one region are unheard of in others. Typical practice in many areas is poured concrete walls - a potentially expensive option if your plans call for concrete block. It's important to know what foundation systems are common where you're building.
But even a house with the proper type of foundation for your site may need to be specifically engineered to accommodate the local soils, and the local building department.
Soils drain and retain water differently, and soils have vastly differently capacities to bear structural loads. In most areas, you'll have to show the building department that your foundation is designed for the local soil conditions.
The Plumber's Credo - "everything flows downhill" is extremely important to remember when designing your home. On a developed lot, the municipal sanitary sewer line is buried near the front (usually) of the lot. The height of this pipe will determine the depth below grade of the basement slab since the effluent from the house must "flow downhill" to the sewer line.
An undeveloped lot is one where the utilities - electricity, water, gas, and public sewer - aren't brought from the street to the buildable area of the lot. On larger undeveloped properties there may not be any public sanitary sewer to connect to at all. On such a lot, you'll need some type of private sanitation system.