Also have a dual purpose room. We did inexpensive white shelving units around two walls, with fabric boxes to stash stuff, (office, and my "crafty" supplies), threw in a few decorative items. Got a tall basket for rolled up mats/foam roller storage, a complementary lower basket to throw in the requisite elastic bands, small hand weights, etc. Decorated walls with pics from our travels, framed with colored mats.

Thanks everyone for your further comments. No problem about it being an old post, always nice to communicate with people about design solutions/problems. Jilly, I posted some photos on 1st January 2016, they appear further up in the post. Garden Beet Pty Ltd, and Morel Construction Ltd, both of your solutions look great, but our problem still remains the western Queensland sun which is pretty vicious on anything that will either wilt, fade or break down. It was quite a difficult challenge to come up with something that was affordable, workable and durable. I would love to have had plants because I believe they soften large "hard" exterior areas, but we have decided that we will do that with pots around the pool area. Still have that to do, even after all this time. :) Thanks everyone for re-igniting this chat. Jilly, hope you find something that works for you.

lucky you! your water tank is below ground. I have to look at my 20,000 litre tank outside my kitchen window. It sits on a concrete plinth so I can't even plant around it. I'm too terrified to grow creeping fig on it incase it affects the integrity of the tank. At the moment it has wisteria draping over it, looks lovely in spring but deciduous and it's now becoming too invasive so need to get rid of it.. I also have star jasmine approaching from an arch beside - can't wait for it to take over the tank.. I love all the decorative features suggested but I reckon something like star jasmine might work with some other landscaping features to the side: bench, rock, more plants. The beauty of star jasmine is that it doesn't root, will drape over and can be pulled aside. Every couple of years I put the blower over the top of my water tank it to make sure the leaves don't mulch to create soil on top.

a bathtub full of water plus a person has a specific weight depending on the size and make of the tub and 1 litres of water weighs 1kg and a bath may hold 100 litres...if the floor under the dormer is the same as the rest of the floor there should be no difference in the weight capacity in any part of the floor and the floor has already been tested by the existing tub..A structural engineer should be able to easily reassure you and/or design suitable reinforcing to install the tub into a wide supporting frame which can distribute the weight over a wider area than a bathtub supported on dainty legs...a new bath mounted in a generous surround should look perfect under the window