Ohio Rev. Code § 4722.04: Down payments.

A home construction service supplier may take as a down payment not more than ten per cent of the contract price before the supplier's performance that is required by the contract begins, except a supplier may take as a down payment not more than seventy-five per cent of the total cost of any special order item that is otherwise not returnable or usable before the supplier's performance that is required by the contract begins. This section does not apply to a home construction service supplier who enters into a cost-plus contract. A supplier may accept payments from a construction loan in connection with a home construction service contract.