I grow quite a lot of borlotti beans, both the bush sort and I have Jiminez, the climbing ones.
If they have gone in as a late space filler, you are best picking them as flat pods and using them as french beans. They are going to run out of time to produce beans for storing.
If they have been in a while and you have pods forming, you have 2 other choices. You can harvest the beans when the pods are swollen, but still not drying out. To store, I blanch and freeze them and they are great for soups, or cooked and used for bean salads.
Otherwise, leave the pods as long as you can on the plants and they naturally turn into dried beans. As long as they are mostly dry, you can finish this process on the windowsill if the weather suddenly goes downhill. Once the pods are dry, shell the beans and you have dried beans that will keep in an airtight container until you need them
As you might gather, I'm a borlotti fan