As always, it depends....
Basically, you can finance everything related to building a house. From the commitment interest to the children's furniture, but....
1. Not every bank does that. This narrows down the selection of banks you can choose from.
2. Furthermore, it worsens your loan-to-value ratio and thus the interest rates. Here we are talking about value-increasing items. That means the house, renovation up to a certain amount, and ancillary construction costs without purchase incidental costs are value-increasing, thus not harmful. All other costs such as furniture, kitchen, commitment interest, etc. (here we are figuratively turning the house upside down and shaking it) worsen or are harmful to the interest rate.