Just about all lenders offer "stage payment" loans for self-build houses. Rates are the same as normal house mortgages so check the Best Buys area on Askaboutmoney.
You'd be advised to get approval for your loan before you start work, so that you know there won't be problems when youve 25% of a house built.
It's vitally important that you get a supervising architect or engineer to supervise all stages of construction from day one. A lender is going to look for confirmation from such an individual that s/he supervised the construction from the very start, before offering a loan secured on this property.
Liam D Ferguson
www.ferga.com