One rule I have, is that they can't use my examples in their poems. However, they can do a slight variation of an idea. I try to make sure that I don't choose the most obvious ideas so that they have some options that are not too difficult to select from.
After giving some examples, I usually get the students to brainstorm ideas on a thinking page. Once they have several to choose from, I get them to add descriptive language and juicy details to their ideas. Then they choose the ones they will use in their framework. They create a draft on plain lined paper, edit it, and then do the final copy. They love having the fancy paper to display the finished poems on the bulletin board.
Here are some samples of scaffold poems from my Teachers Pay Teachers store. Click on the images to get your free copies.