Seed Capital not going far enough to begin construction

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Hi, I am having an issue wrapping my head around this. I use my seed capital as a deposit on my new home build loan, I then receive the money in one lump from the bank, and have to use these funds to build the home, market and sell. When do you usually have to start paying off the loan? Do you use the loan itself to pay the loan off while simultaneously building to sell? Or should you have a side hustle to deal with the interest payments? I am struggling to wrap my head around this, can someone please spell this out in Layman's terms?