Hi Sue, I think it would look amazing if you used some tiles with a bit of texture. The wood look tiles that are popular at the moment would be an example. If you chose a colour that toned in with your floor you would get a really nice cohesive look but with a bit of interest. I've attached a photo of a recent design of mine as an example. Just a suggestion!

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.

Are you tiling the shower base? If so the larger the tile then the more cut tiles will be needed to get the drainage right to direct water to the floor waste. If it is a small bathroom make sure that your tiler aligns the grout lines on the floor with the grout lines on the wall. If they are slightly offset they look pretty bad. Would you consider using the same 300x600 tile on the floor and wall? If so then lay the tiles horizontally, not vertically. However with any good tiling job the better, flatter and straighter the wall is before tiling will result in a better result. Don't expect your tiler to make a perfect job if the walls are not perfect before they start! Best of luck Dr Retro of Dr Retro House Calls and Dr Retro Virtual Visits

we had shower drains custom made from by on line company called myshowergrateshop, i later found that the local tile suppliers could have also supplied custom sizes and our tiler was also able to easily reduce the size of one extra long grate to suit a change of plan