Transferring ownership may have hard results. If you transfer the ownership but the recipient doesn't have enough free space , none of you can see the files and the only option is to upgrade the account. which is like telling a customer that isn't happy with a product to buy another one :()
I believe that the minimum is that the user will receive a notification when changing ownership saying someting like - "Please make sure the new owner has enough space to receive the folder".
A more proffesional solution is to display a message allowing the original owner to cancel the transfer.