Structuring a lease option

Have a client who has property to lease but would consider a lease option. My understanding is that we would do a TREC lease and have an attorney do the terms for the option. But what kind of terms.
Do TB pay a down payment and security deposit? Or is there just an option fee? Historically, how is that amount determined? A percentage of the purchase price, the monthly lease amount, etc?
This would probably be for a long-term lease before the option would be exercised.
thanks in TX