Hi George30
I would say that the bank will look for you to have 10 to 15% of the cost of the build in savings.
The amount you get might be 4 x your salary and 3 x your partners. Other way they used to calculate approval was that repayments could not be more than 40% of your combined take home pay. Not sure if these rules still apply. You will both need permanent jobs to get a mortgage now.
Its also usually a good idea to have 10% of the cost to allow for things that go wrong or when you go over budget.
The bank will also require your architect or engineer to complete an estiamted cost of the build and sign this off. Eg costs of the base, blocks to roof level, roof, first fix electrical/plumbing etc, 2nd fix etc etc.
Even if you qualify for say €150K for example they will still only loan you the costs of the build, which you reckon is €130/140 k.
maybe make an appointment with each of the banks and see what they have to say. Might be worthwhile going through a broker to get the best interest rate.
Make sure you solicitor has good experience of self builds so it doesn't slow you up waiting on stage payment cheques