I'm in tile retail and the most popular size for large areas domestically is 600x 600. The large sizes are gradually becoming more common but no where near the colour range of the smaller sizes. The only advantage of the larger size is less grout, but this wouldn't be much in a domestic size room. The most important thing to remember is how will they be cut in a room or a hallway. You don't want a giant tile then a 150mm slither down the hall. If you consider the larger tiles remember they are unforgiving if your floors are not that level. Laying costs may also be higher.

unless you have a very big bathroom the actual laying of the tiles could be the smallest cost of the whole renovation (what is the size of the space?)...there's also the removal of the old finish (and any old asbestos) and preparation of the new surfaces and waterproofing and any new fixtures and tile glue and trims and grout...ask the tiler what is included for the price

Yes, siriuskey. You are right again. It would be smart to invest in having a professional draftsman draw it up. But on face value, I really think oklouise's plan works. I have sort of drawn it out on the floor. I love that she is using standard size vanities with only a custom made top, and the towel shelves are now 450 instead of 250 wide, which is much better. The little odd-shaped infill at the end of the bath provides a spot for the lovely jug and bowl set my mother made for me. (I used to use the jug to pour water over the grandchildren's heads when I washed their hair, and now it's just a lovely decorative item with deep sentimental value) and there is space beside the bath for the urn filled with decorative soaps that was a gift from a son-in-law on his first visit to our home. I really think the bath needs to come back to 1500 long, but that's not an issue at all. I found a really nice shaped oval tub at 1500 x 760 that I like and is quite inexpensive. I don't need to worry about towel rails because I have a lovely timber free-standing towel rack that will fit nicely at the end of the shower if the shower door is placed on the side. It looks like the vanity drain can run under the drawers and into the bath outlet and the WC vanity will run under the wall into the shower drain, and all other plumbing stays the same except I'll ask the plumber to chase the shower tap and rose into the exterior wall rather than have it on the side, OR there is room for a false wall in front of the exterior wall to hide the plumbing if that works out better. The niche can go in the new wall behind the WC vanity. I'll be really surprised if this isn't a feasible plan, but I will take your advice, siriuskey, and get a pro to draw it up so I can be totally confident it works. Can't thank you enough, oklouise - and you, siriuskey, for all your efforts which, I think, contributed by generating new ideas and flushing out the important issues.

Is there a reason you’ve chosen a nib wall instead of glass? Glass would open up the bathroom. I think your plumber will also change the location of your drain. And unless you absolutely absolutely love the long shower grate, I’d skip it. They drain into the same size hole as a standard one but add a larger area to clean and catch hair. I would also out the toilet between the vanity and shower. A toilet needs room on both sides but a vanity can go hard against the wall maximising the space.