Hi Clare. it might help if you upload a plan and then you tend to get more feedback.

I think the smallest size shower is 700 so would probably use that as a minimum although that's for a fully enclosed shower so you could potentially go a tiny bit smaller if stuck for space. It does also depend on your family's size though as to what is comfortable for everyone. I'd also include the niches for shampoo bottles etc if possible

I've just got a 760x760 shower and it's fine for us. The room is 327 x97 (they must have lost a fair bit with tiling and plumbing). My previous ensuite was a similar size with the same size shower. We fitted our old ensuite and the priority for me was a really good shower rather than a teaspoon of water over your head! I know you may look a bit mad but you could go to a showroom and try getting in a cubicle! Or see if any friends have the same size as I think you'll need the extra space for getting ready but it does obviously also depend on the height and build of your family

Building a pergola can be a fun project. Based on the photo, it seems like the posts could indeed be 4"x4". As for the frame and Metal Joists, it's a bit difficult to tell from the picture alone, but I would suggest using 2"x6" or 2"x8" timbers for the frame and joists. These dimensions should provide sufficient strength for your pergola. Now, when it comes to fastening the frame to the posts, L brackets can definitely be an option, but there are other methods you could consider as well. One popular choice is using metal joist hangers. These are specifically designed for securing joists to beams or posts. They provide a strong and reliable connection, ensuring the stability of your pergola.