Is it permissible to take out a loan to build a plot of land and postpone marriage for three years, or is it better to marry and live in a rented apartment and postpone construction for 18 years, knowing that the borrower is at war with Allah?

Striving to build a home while being able to rent is not among the necessities that permit borrowing with usury (riba), because the need is for a suitable dwelling. If it is possible to obtain it without falling into usury, then committing the forbidden act is impermissible. It is better to hasten marriage while renting a suitable dwelling without usury, and Allah will provide a way out for building the house. If it is possible to delay marriage until the dwelling is built, there is no objection. It is recommended to frequently engage in dhikr (remembrance of Allah), istighfar (seeking forgiveness), and fasting.