Everyone will quote you a figure per square metre. The problem is not the figure, it is what is missing from it.

What it usually includes
Structure, envelope, roof, first-fix services. That is, a house you cannot yet live in.

What is always forgotten
Utility connections — they can exceed €10,000 if the network is far away. Earthworks, if the plot slopes. Fencing. Landscaping. And, almost always, the kitchen.

Why the technical design matters
Without it, every builder quotes something different and you compare apples to pears. With it, quotes are compared against the same bill of quantities, and the differences become real.

The contingency
Set aside 10% of the budget for the unforeseen. This is not pessimism, it is statistics: on one house in three something appears that could not be seen before digging.

The design fee
Between 5% and 8% of the investment. It sounds like a lot until the first build quote on a poor design, when the spread between builders is several times the fee.