quote for stone gardenroom

[backfromoz]

We have the ruin of an old stable in the back garden 2 walls of which are still standing. We need some storage space so decided to rebuild it.In the future itll be a playroom for the kids when the music gets too loud!.A lot of the orinigal stone remains which we intend to use.It will be 18sq metres and have a lean to slate roof and 1 window. Ive been quoted 14k for the job inc vat. Does this sound reasonable. It seems a lot to me esp when the stone is provided by us?
appreciate any advice