Betty: To insure success in your building project, you could hire an architect to draw up a set of plans that will be acceptable to those nice folks down at City Hall. You then could sub-contract the carpentry, plumbing, electrical , tile, dry wall and painting to known profesionals in your area that have a good batting average with satisfied customers.
Or you can gather up your courage like millions of other do-it-yourselfers in this country and have a go at it. Seek the wisdom of the elders in each of the disciplines involved in the undertaking. Do your homework and organize your efforts, and then have a good time while improving your lifestyle as well as your real estate value.
Lots of luck.....Bud