OK here we go - in broad sections starting from the ground up!!
EXTERNALLY
Foundations £390 (no concrete here used eco grids)
4x2 framing £400
6x2 roof joists £222
wall OSB board £169
Membrane £60
Laths £58
HardiPlank £1540
Roof decking £166
EPDM membrane
and trims £600
Soffit and fascias £126
Window £60
french door set £345
Screws £22
Guttering £30
INSIDE
Rockwool RWA45 mm inuslation batts 50mm to walls and floor 100mm in roof space £338
Wall timbers and £300
flooring
Plasterboards £200
Consumer unit 10 way£45
Cabling £100
Laminate floor £118
Skirting & Door £75
paint £30
all electrics which include sauna, pinshcak and workshop
2 x smoke alarms, 2 x PIRs, 12 sockets, 2 switches, 13 backboxes, 18 downlights, LED flood, emergency lights, 6 ip65 soffit lights, 2x soffit spks, 1 IP camera, 1 IP POE switch,
2 x 1.5kw oil radiator, 2 x sauna spks, 1 sauna fan, 1 PIR light switch
total for elecs = £518
EDIT
missed off 10mm SWA Cable, ethernet cable and alarm cables back to house
£133
GRAND TOTAL = £6045 (does include some no pinshack bits ie sauna stuff)
Cheers
kev