Check all parts are present. - You should have ten pieces.
1 x roof
1 x rectangle facia
8 x posts
Remove excesses and file or sand where necessary.
On inspection you will notice that 4 posts are longer than the other four. You can create your hay shed to have a sloping roof or parallel to the ground. Trim the longer posts to your desired length. Glue posts to the inside of the facia. Paint.
Glue roof to frame.