There are tons of threads here on workbenches. As to portable, depends on what you need. You might have to weed through the searches to find something that suits your needs.
This will take you to the image search page for workbenches. I would gather inspiration from these pictures and look for the features you most want incorporate. Everyone uses their work bench differently, like room for a refrigerator or use of a table saw. Like yourself you wanted to build something small and portable. What kind of space and size of the area do you have to work with?