I started out building coco-leles and have done many of them. The best thing you can do is to locate the biggest coconuts you can find. The Samoan varieties can be huge, double the size of the more common ones. Thin and smooth the shell as best you can, especially the insides. You can fiber glass two or three shells together if you fit them properly (I used to build tenors using three nuts; one large one for the upper bout and two smaller ones for the lower.) The most difficult part will be in fitting the neck and getting it true. It's fun project as long as your expectations aren't too lofty.
