Can I write my own business contract?

You can write your own business contract, and for routine client work it is standard practice. The law cares that the agreement has offer, acceptance, consideration, and capable parties, not who typed it.

Self-drafting works well for service agreements, small sales, and simple collaborations. It fails at the edges: complex IP transfers, equity deals, regulated industries, and anything where losing would genuinely hurt. Those deserve a lawyer's review, which costs far less than a lawsuit.

If you draft your own agreement, do not start from a blank page. Start from a vetted structure so the boring-but-critical clauses, payment terms, ownership, liability, and termination, are already asked for. You supply the facts; the structure supplies the completeness.

That is exactly what a fill-the-fields contract maker is for.