Screen should be 1200 without ledge. Ledge say 250-300 brings your shower head out further adding to dimension of spray. Would need an aluminum window watertight.

Hi Kate

Here is my other bathroom

1000x1000

here is a 250mm floating ledge (not sure if you can float 250mm out from a single internal brick wall but it could also be non floating)

So its just too small with only 750mm standing room left?

When you say "Screen should be 1200 without ledge. Ledge say 250-300 brings your shower head out further adding to dimension of spray."

Are you saying then i would need 1200+250 = 1450 for a walk in shower with 250 ledge?

Would need an aluminum window watertight.

at this stage we already have a double hung 562mm wide aluminium window already made we intend to slot in. It would start right next to the end of the 1000mm from that corner, Its aluminium but given double hung as parts sliding up and down its probably not watertight.

Yes you need 1200 for walk in shower plus ledge width, 250 = 1450. Unless you are going to sit on ledge while showering, you will need to extend shower head out, or have a rain shower.