Hello, It looks like you have your work cut out for you. I would like to introduce our product that could be of use in your application. We manufacture Landscape Tanks. They are a Retaining Wall, Garden bed and Water Tank all in one. See Some example pictures below of how our tanks have been utilized in a similar application; To see more examples please click on the link below; http://landscapetanks.com.au/gallery/pool-surrounds-fences/

I would also suggest a deck at the same level as the house floor. Merbau decking boards are hard wearing and reasonably priced $. Also look at a new sliding doors with insect screen built into the door frame as a second door. This will introduce cross ventilation and keep the mozzies at bay in the night and make your internal floor space appear bigger. I would also build a veranda over the deck and mimic the existing gable end of the roof ( keep the rafters high ) and use all laserlight transparent roofing material to keep natural light flooding in. You could also look at introducing a natural gas point and some outdoor power points for gas BBQ and entertaining. The space will effectively become your new Outdoor room - enjoy :-)

Ok great, any idea of colour? I would love to go clear can imagine it being too hot

Yes, you will need council approval. You are enclosing and extending an outdoor space. Contact your council and see whether you actually have room on your block, (open space to building ratio) to legally enclose that area. You would need to add a roof correctly by integrating it into the existing roof. Maybe you could have a slightly angled flat roof?? Regarding the drain. This would be a soak well for water dispersion. The bricks pavers will all be pulled up prior to construction of new concrete slab. Soak well and drain would be moved to boundary. However, all of the above is only possible if the council application is approved. Regarding cost, to do it properly, which is how it should be done, allow for $3000 per square metre.