Used to have a pergola with grape vines and recently came across these guys. You can see from the image below it looks really good in a garden:
If you are looking to build a pergola and aren't sure in future I would recommend a call to them as they can send out full aluminium pergola kits for you to make yourself if interested and you don't have to worry about not knowing what to do.
You can see more information about their products
here