So, what else is kicking around on the floor of the shed:
More small bits of ply that can be used as formers, some scrap small cardboard boxes left over from Christmas presents, and a pile of paper towels in the corner (paper towels are not so widely available these days, but when I see them I always stick a slack handfull in my pocket).
Can you see what it is going to be yet
The paper towels have been brushed before applying with a weak mixture of wood glue and water. Once dried it will be hard but still very light. A bit of paint and grass and it will look the part.