I have been looking for an engineer to act as PSDP for a small (ca 20m2) single storey extension of a terraced house). I would also like them to sign off re: building regulations. It's a very straightforward job and we already have drawings that we submitted for planning (was needed in this case) and the builder is happy to work off. How much can I expect this to cost? Are there any ways to save on these fees?