Am I obligated to help my father complete the construction of his house, which he cannot finish on his own, especially since he still has loans, and is it more appropriate for me to save money or to help him with the small amount remaining from my salary after my family's expenses?

Repaying a father's debt is not obligatory for a son, but it is commendable. Buying a house for a father is not part of the obligatory financial support a son must provide when the father is in need, because the need for housing can be met by renting a residence. Therefore, you are not obligated to help your father with your money to complete the building of his house. However, it is commendable, and we advise you to do so as long as you are able, without harming yourself or your family, for being good to one's father is one of the best deeds and most beloved to Allah Almighty.