When i was having my single story extension built 6 years ago the usual guy I used told me it would take 10 days for 2 brickies and a labourer. Then one of the guys I work with said his mate was looking for a job and he was a bricklayer he turned up asked for a pen and a sheet of paper, did a quote gave me a list of everthing he needed. and a price £800 cheaper than the other guy.
He started the following day and did it all by himself including mixing and loading and 7 days later I was the proud owner of all the brickwork shell of a 8 mtr x 4 mtr single story extension.
All I did was make sure everthing he needed was there for him when he needed it, the cost £1100.
The only other thing I did not do was the plastering everthing else I did myself.
The total cost of the extension less than £10000.