Just quick prices so far:

Building, planning consent: £185
Building control: £440
New 14.5ft door: £1850
Composite door: £500
Window: £100
Highways consent for drop kerbs: £230
Land clearance and prep: £800
Blocks,bricks,cement etc appx: £2500
Readymix concrete 12 cubic mtrs: £1000
3x heavy duty lintels: £450
5x large bags building sand: £165
Scaffold: £300
Velux, probably another 2 though: £200
Builder if was paying him: £2000
AtticTrusses load bearing x16: £2100
9x drop kerbs and new driveway: £1800
channel drainage: £150
Fascias,drainpipes etc not sure
new 5tonne rating manhole cover:£120
Roof,ridge and cloke tiles, lats. £600
Reinforcing bar meshx4 sheets: £120
2x handcrafted corner stones: £120
10 tonne class 1 hardcore: £150


Probably other little stuff ive forgotten.

So probably some where in region of £13000 there. So realistically with other stuff not known yet i would say some where close to the £15k region.
ive done quite a lot of work on it myself and will continue to do so.

Ive tried to keep costs down but things are so expensive to buy now.
I have no doubt it could have been done cheaper, doors etc.