building our own 4 bed house on a plot of land

Running_Horse

Agreed. You would be wise to invest in an architect and project manager. It will save you money and mistakes.

lightSwitch_3

I think that 200sqm should be your minimum 100+100. Say 8m by 14 m. This will give you a nice wide hall with wide rooms. Always think of width, narrow room are ugly and unpractical.

Keep in mind and spend a few extra grand to make it as energy efficient as possible and stick your fingers up at the avaricious energy companies and the Chancellor. Gas will become very expensive in the near future. People will be switching off their boiler to have money left to eat.

JQ.

To work out how much to pay for the land, work out the value of the completed house and deduct the following:

Build costs (make sure these are accurate, £120k sounds light)
Purchase costs (stamp and fees - sol & surv)
Fees (planning, architect, QS, Project management)
Finance costs (mortgage and Project Monitoring costs if the bank are providing the development finance)
Contingency (2-5% of costs)
Developers profit (20% of costs)

The answer is the land value.

If you get any of the above slightly wrong it can end up costing you alot in the long run - so it is important that you get this research part right. Get the costs professionally calculated.

You can reduce the developers profit because you're going to end up living in the house yourself, however, why bother going through this whole process if you don't make any money at the end of it - plus if you do reduce it all you'll be doing is giving the vendor the profit for all the hard work you're about to do.