London this year, L-shaped on a small Victorian terrace. We've got one bedroom with dormer over the main house and a separate full-size bathroom over the back bathroom.
£63,500 so far, vs initial quote of £40K.
The £40K covers paperwork, scaffolding and skips, a new slate roof, construction, plumbing and electrics including smoke alarms in the rest of the house, finishing to bare wood and plaster, and bathroom fitting but not the bathroom suite, tiles or tiling.
The cost on top is the bathroom suite and tiles, bedroom furniture, carpets and painting, having an aerial fitted while we had easy access, and about £4.5K on a mist system and fire door for downstairs.
The upstairs is finished but the new stairs are still bare wood and plaster, so I think we will finish about 65K.
So the EA is right in that the quote for the core work is about £35K + VAT, but you'll need to consider the cost of decoration and (if you want a bathroom) bathroom suite on top.