What is the correct action regarding the parents' usual request for money despite his need to save for building a house, and is the husband's refusal considered a sin against his parents?

A son should spend on his parents and be dutiful to them. However, he is not obligated to spend on them if they are not in need. If they are spending money on unnecessary things, he should advise them gently and kindly, and inform them of his need for money to build a home. He is not obligated to give them everything they desire. He may use dissimulation by entrusting the money to someone he trusts and informing his parents that he does not have money available.