Do you have a good idea of how many bed rooms you want, the size of your kitchen and the appliances that you need in it, how big is your pantry, dining room and living room, family or entertainment room? Do you want a basement and / or two stories? Utility room or hide the utilities in the wall?
Then you need to consider climate, snow, rain, sun, wind, tides, and hazards like earthquakes, tornadoes, fire, hurricanes, hail and sinkholes.
Will you want guest rooms? Will the kids need space for homework and play space indoors? How much storage space will you need? (closets)
Will your garage be just for cars or trucks or will you be packing it full of garden tools? Will you need a separate shop to work on cars and other projects? Will the garage be attached or free standing?
Each item can change the home you will build and how it is constructed.
For me my top concerns were earthquake, fire, and snow loads, followed by wind. Most of the concerns for earthquakes took care of wind but I had to add for snow loads. Exterior finish had to be adjusted to make it as fire resistant as I wanted. (stone and brick are ruled out by earthquake specs) It is just my wife and I but we would expect the kids to visit so I planned on 4 bedrooms and 5 baths. All the bedrooms have baths included but we need a guest bath.
I drew up the separate rooms - and cut them down as needed and fit it into a rectangular floor pan that is no more than twice as long as it is wide because that is the most stable shape for earthquakes - no 90 degree bends and no kick-outs - just a boring rectangle. Considering our ages I designed it to meet ADA specifications.