how to build a low cost boat?

i need a durable boat made of cheapest fiber glass and cardboard.?

Make the frame out of 4" PVC pipe, then line it with the cheapest thing that won't crack from your weight.
rickharris8 years ago simple and light and quick to build - you can cover in Fiber glass if you like.
Check out these instructables:

How to fiber glass - used to fix a kite board but it's a great instructable on actually fiber glass things.

Building a little row boat

Building a greenland kayak

Cozy boat part 2

Have a look through those for ideas on building a boat, I'm considering building one myself, just for fun...