New garage with deck over - materials?

My PPOR needs a new double garage, and the placement means I can use the roof as a deck straight off the living room. Obviously the deck needs to be fully waterproof, and in the future I'd probably like to build an orangery or conservatory on it.

Has anyone done this before?
Any thoughts on materials for sides and roof?
Price?

 

May even be cheaper to build over the garage and with a roof it allows greater floorspace from the living room and may enhance space and value for no real cost, different flooring materials (ie timber not a reinforced slab and no floor waterproofing will contain costs. A range of design choices affected by property streetscape etc subject to Council as well as site eg steel v's block etc.

A neighbouring house did this recently. Started as a double garage concept. Then a slab entertaining area above and then found it cheaper to build out over the garage for same $.

 

Thanks Paul. Good idea - I was going to enclose later but it may be more cost effective to do it in one go.