Hi, Trish K,
You are going to receive many responses to your question! Weather patterns are definitely changeable. A lot will depend on where in Scotland you're going, and what you plan to do. I've been in Aberdeen in early July when it was so cold that Mrs. A had to buy a winter jacket. Fortunately, as it was summer, the winter jackets were on half price sale!
Waterproof shoes are a big help, especially if you're going to be outdoors a lot. We've been able to get by quite well with Merrell low waterproof hiking shoes. Others will have a specific brand preference.
Long pants aren't absolutely necessary. However, if you're going to be hiking in the Highlands and Islands, they act to keep the midges at bay. If you don't mind being a bit cold, shorts with a pair of lightweight rain pants would be sufficient. If you plan to visit any "fine dining" establishments or church services, then long pants would be in order.
Some sort of waterproof lightweight jacket would be helpful. You can always layer up. If you need something warmer underneath the jacket, and you didn't bring anything with you, you can always find a sweatshirt or a hoodie in a charity shop. I have a nice collection of said garments, and the most I ever paid was six pounds.
Congratulations on visiting Scotland for the first time. You are going to love it! As I always say, visits to Scotland are like potato chips - you can't have just one!
Best wishes,
Mike (Auchterless)