My old man's a builder and I have had a fair bit of experience working with him, our place is currently undergoing some pretty major renovations. The Laundry, Bathroom, the Toilet, and bed rooms were all gutted back to bare frames. The hardest part of an extension with a stumped house is the floor and wall lines are never perfect anymore so it's very difficult to line up the new walls and floors! The bathroom is being tiled at them moment and looks awesome, laundry is done with a new storage room and we put down solid boards on the floor with hidden nails in the bedroom with the addition of a walk in robe. Overall it's a lot of work but the results are well worth while, just make sure that if your going to do it that your working with a realistic time line and not trying to rush it as trying to find time can be hard at times!