I roughly sketched outlines onto the cardboard with a pencil and then cut them out. We glued all the bits together using a hot glue gun. (This was probably the highlight for Nicholas, he asked if he could have a glue gun for his birthday!).
We made the mast out of a kebab stick and a paddle pop stick. I cut the sharpish end of the stick off after we had used it to puncture holes through the cardboard and the sail.