Estimates of extension costs (any ideas?)

[Likely Pigeon]

Hi, not sure if this is the best place for this but here goes.
Just wondered if anyone had a rough idea of costs for building an extension. Would be for a 2 storey side ext on detached house. Pitched slate roof with 1 dormer to be built. Size 3.5 x 7m. Knocking through from existing rooms to extension on both ground and 1st floors.
We are based in Scotland, any ideas would be appreciated.

 

[freddiemercurystwin]

Around £1200 per m² per floor, allow say £3K for breaking through + fees (architectural technician + structural engineer + building control etc). So say approximately £64K.