Well a really good way to get a really straight and easy POD would be to use a pot for plants that is tappered. Cover it with wax paper and then cover it with 2 oz glass cloth and epoxy. Do that 3 times and you will have a really strong POD cone that you can add your formers to it. If you cannot find the write POT take a couple of pieces of styrofoam glue them together and carve one out that has the proper shape. Then do the same thing as before to glass it.

If you want a good to make sure that the pod builds straight with wood make sure that the stringers are exactly the same lenght before you start building the POD. Then you can be sure that the rings and formers are always straight. You just need to make sure the first former is 90 degrees to the building board and the rest will fall in place.

Enjoy!