can you make a boat from any non-porous material ?

As long as the possible water displacement by the "boat" weighs less than the boat itself it should float. The material also must not break with the force of water exerted on the outer hull.... 1/8th inch glass wouldn't fare too well on anything very large.

YES: Battleships are made of steel as are subs, any metal will float if it is made right to displace enough water to float the craft!

Yes, anything, so long as it displaces more mass of  water than its mass.  In other words, a big enough hole in it.  Even that which dissolves in water, like salt/sugar can, if sealed.  Many boats are made of porous  material, like Wood? That is what shellac,  spar varnish, oakum and tar were used for.

Those  noodles for pools are Closed Cell, Non Porous. Try  a sponge or  foam rubber---sinks. Sealed with Varathane--Doesn't. 

Most, yes. But if it dissolves in water, like sugar or salt, no.

You can even make a boat from some porous materials, if they are sealed. Wood is porous. Ferro-cement is common in sailboat hulls.

The boat has to weigh less than the water it displaces.

As long as the "boat" displaces an equivalent amount of water, yes.

Provided the overall density of the whole boat is less that that of water it will float

You can even make a concrete boat.

The 'Noodles' that you find around swimming pools are very porous, but float well

it all depends on buoyancy