In order to build something "suitable" for the person you're selling it to, you have to know a lot about the person. For example, a home built on pilings for a flood prone location would not be suitable for a person in a wheelchair unless you provided a method of access that would withstand water. In fact, any stairs would not work well in that situation.
Start with the needs of the buyer. For ground level access, a concrete slab will work if flooding isn't a problem. An above grade foundation for areas where there is a minor risk of flooding and pilings where the risk is high.
Next, draw a floor plan. consider the width of door openings and height of cabinets for any special needs occupants.
Calculate the number of square feet of the building and the cost from an Internet site like:
http://www.home-cost.com/construction-cost-per-sf.html
Note that you must select the area where you live, costs are different from one location to another.
Make sure and look up the cost of extra features added for special needs.
Add your percentage of profit. Example: If you expect to make 10 percent, multiply the cost by 1.1.
Answered Oct 01, 2011
Edited Oct 01, 2011