I made a Pinterest board, specifically for it, when out eldest got married. I then spent time touring the shops on the net looking for possible purchases I liked, pinning them , going back and looking at them and compiling my outfit that way.
I started with the idea or the colours I wanted and worked it from there. Don't forget to include a Fascinater/headwear if you are having one.
My clothing came from Debenhams (shoes and Fascinater) John Lewis (dress) Marks & Spencer's (wrap and underwear) and online I bought the parasol and accessories. I also had a warmer lightweight jacket, I didn't need in the end. I bought it as a back up incase it was cold. It was August last year and I bought it incase it was cold. That was from Joe Browns.
Hope some of this will give you some ideas to get you thinking. Oh and don't forget to think about hair and make up.
Most of all enjoy your lovely day at your daughter's wedding