There are too many variables to quote.
As mentioned draw something up people can read, measure length of foundations, number and size of timber bits, windows wanted etc etc.
And get prices.
I would start differently.
- sketch needs building
- look for windows, door frames etc and purchase or pickup same.
- start excavation of foundation trench and complete
- add reinforced
concrete ring to top
- source cob materials and cost them if need be
- when most bits are around get things happening.
- purchase things as you have the funds