As you can see by the diagram, wood floats, which means it is less dense then water. Making a boat out of wood could be a good idea, as long as it is not too heavy. If the wood is heavier than the water the wood will not float.
this video from the show Mythbusters explains Archimedes principle and is really helpful, they also put weights and water in a normal size boat and explain that once a boat tips over it will not work as a makeshift submarine.
you could always make your boat out of recycled materials. on this website they show you how to make a boat out of a soda can and straws and some other materials.