Design Development is where the home begins to take shape. All of the information gathered in the Pre-Design is put to paper. "Form follows function" is a common phrase made famous by the architect Louis Sullivan. Simply put this implies that the shape and style of a building will be determined and designed by its use and logical flow. There should be a logical progression to your home. You wouldn't want to carry your meal from the kitchen through the living room to the dining area. The dining area should be in close proximity to where the food is actually prepared. I beleive that the saying "Form follows function should be carried one step further, "Form follows function, led by fit". Unless you have an unrestricted budget on a large parcel of land, the home must be designed within the space that you are restricted. Most people have restrictions of some type, either a budget to stay within or a lot size they must build within. Often it is both. The local building department will also have restrictions for your structure, such as how far you must stay away from your property line and how high your building can be.
You will be presented with a series of site plans, floor plans and exterior elevations to review and comment on. Design Development is the time to create the home of your dreams within your budget. Trying to redesign your home during construction is very expensive.