Hi Paul In apartments, the killer for layout changes are always drains, then water supply, then load bearing walls. Before you consider doing any changes to the layout, I would advise you to locate the drains (pics would be good) as they will likely restrict you. The drains are important for obvious reasons but also important is the fall (ie downward slope) of any drain you wish to install in a separate location. It means you have to take into account more height the further away from the existing drain you go. It is likely that your existing laundry trough/basin has a drain going down to the floor, and this is going to interfere with the proposed ensuite entry location. Ditto if it is going into the wall. The big one is the new shower. It will need to have a 50mm waste (drain) in the centre of where your washing machine now is.... and the question is where is it going to go.... I would suggest swapping the vanity and shower over to access the existing trough waste if it is large enough. In a lot of these older apartment buildings, the waste sizes are down at 38mm, which is not going to drain fast enough for a shower. If your existing waste is that size, you will need to have a hob to the shower as it will fill up, and you will also need to check health regs to see if it is allowed in your state. To get the drain for the new ensuite vanity and new laundrette sorted, I would punch through the new kitchen wall and run drainage along the wall behind the new cupboards and around to the existing kitchen sink waste. This will give you plenty of fall and a place to hide the pipes. For the new basin to the existing, you will need to see if you can get it around to the existing basin waste in the bathroom adjacent by running it around and under the bath. Cheers

I would ask the builder about the best solution for the windows in the new ens and laundry as it will depend on the wall structure and waterproofing requirements but it should be more cost effective to install two windows side by side in the old laundry window opening as the windows would need to be ready to install as the old Window is removed and new dividing walls installed ..and, as i would be reluctant to remove the external laundry door, i suggest a tall storage cabinet against the bathroom wall with the ironing board on the external wall and if you decide to lose the door add extra storage in front of the door

I think you should explore the idea of getting a Pod on the deck. its like a mini granny flat / cabana with toilet and small multi purpose room. You might have the space for this. Your layout looks fine as it is, and if you have a covered pergola, a second toilet in a pod will works well there. I am a bit against adding plumbing and moving walls to your house. First its a mess. lots of putting pipes under the flooring, fixing the flooring again, also ceiling and conrice works, and you end up with smaller bed, tighter layout. Too much sacrifice and not too much to gain.

the measurements look more like a hallway space..challenging but never impossible and any internal room can always be improved with my favourite Solar Skylights (try Illume or Arcol brand available at major hardware stores) but, if you're planning to retile and adding another room there's no better opportunity to see if there's any opportunity to rearrange the space to a more comfortable shape..post a plan including of all the adjoining rooms and the new room