One of the most common tenant improvements that landlord pay for in a commercial lease is a tenant lease improvement allowance. The changes that a tenant asks for should fit within those pre-arranged means. If the cost of improvements exceeds that TI allowance, the tenant must pay the difference. Usually, those numbers breakdown by price-per-square-foot or a total sum. Some landlords are flexible and willing to negotiate the TI allowance, especially if the rental market is doing well.