This month's column is taken from the author's correspondence with a young couple wishing to expand a small house for a growing family. The house is sited on a tight lot in a town with stringent zoning restrictions. Dear Roger and Kate: Recapping, you sent me your plans, photos, detailed program, and a first stab at a solution by another designer. His work and your constrained budget led me to my first solution, which simply added the ell on the front. Then you told me you would probably go ahead and add to the back, because you could do a lot of the work yourself to hold down the square-foot cost, so I decided to try for