This layout is specifically designed to handle donations, with the ability for the user to choose their own amount. Any Item on this page that has its' price set to $0 will allow the user to enter their own donation amount. For example, you can create pages where there is a $5, $10, $15, and choose your own amount option.  Another option would be to create three $0 Items for different projects...then you could allow the user to choose their own amount and track donations by project. Item 100906 at the bottom of the page is an example of the choose your own price option.