How will handle the walls and waterproofing the whole magilla?

I was thinking just buy a "kit" wall for two wall sides and glass door. for the other two sides

Its not that simple. Post up a floor plan with all dimensions.

No, you can not do that. The pan integrates into the walls. And you would need something very very custom to use the same drain location. Plus, you cannot come within 6" of the radiant heat in your floor in your expansion. So you would need an IR map of that, before even starting to plan this.

Bummer! But thanks for all the replys, you saved me a lot of time:)