basics1_wood.gif
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.

http://videos.howstuffworks.com/discovery/6540-mythbusters-lets-talk-buoyancy-video.htm
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.

http://www.associatedcontent.com/article/795457/make_a_toy_boat_out_of_recycled_parts.html?cat=24
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.