A really great place to get different kinds of felt peices is at teacher supply stores. I worked at a preschool and would go there all the time. They have already cut out felt peices, simple shapes....or they have ones you can cut out yourself but are like stories. If you ever went to Sunday School and saw the story of Noah, or something like that and the felt people look like actual people....the boat looks like a boat, all the details and everything. That is the kind you can cut out. They have all sorts of stories, not just bible stories....they are also great quality.
We made a flannel board at the preschool this is how it was done:
You take a box with a lid that is attached on one side...think about an ice cream box only bigger and flatter. Then you take a peice of Felt a little bigger than the box, and hot glue it onto the inside rim of the box. Voila, you are done, put the shapes of felt into the box and now it's portable.
It also makes a great quiet time activity when a child is too old for naps but needs some rest. That's what we used it for at the preschool