for your average house and budget
Find other self-builders in your area, ask them for recommendations, write short letter with copy of plans to that builder. He will usually ring you with a ballpark price and if you’re interested then you negotiate further and draw up a contract. Try to keep it simple, get yourself a Quantity Surveyor to do a bill of quantities on the house which should then guide your negotiations when it comes to insulation standards, fittings etc etc. Remember standard quotes from builders include things like bathroom suites which cost them less than €300 euro and internal doors which cost them €50. The real bargaining comes in when you want better quality fittings