The landlord must permit reasonable modifications necessary to afford the disabled tenant full enjoyment of the property, such as the modifications described.
To protect both parties, the lease they sign should address who will arrange for the modifications, who will make decisions regarding workmen and materials, and who will pay for the modifications. For example, the lease may provide that the tenant will pay the cost either directly to any contractor or by reimbursement to the landlord, or the lease may provide that the landlord will make the modifications in exchange for a concession, such as an increase in the rent based on the cost of the modifications.
The lease should also cover whether the property will be restored when the tenant moves out and, if it will, who will pay for the cost of such restoration.