We haven't added on to our house but I really wish we could we desperately need more space. We have a small (1400 sq. ft. not including the basement family room) 3 bedroom rowhouse. I have Shannon & Katie sharing a room right now and Molly is going to have to go in there too since Erin is so much older (8, 11 & 14 years older than her younger sisters) and needs her own room. There really isn't much room to extend though so we are probably stuck with what we have. We can't afford to buy a bigger house in the city and we have to stay in Philadelphia because my DH is a Philadelphia Police Detective and there is residency requirement that says we have to live within the city limits
Good luck with your home addition. If we could extend we have friends that could help us build on but the permits to do what we want to do would be really hard to get.