Well you could take an antique or vintage parasol in serious need of a refurb, or when in need of time and on your first go... do as I do and buy a cheap childrens umbrella and use the original cover as a pattern.
Here's a step by step! http://pics.livejournal.com/degracieuse ... y/0002pdk3
Anyone who lives within their means suffers from a lack of imagination. Oscar Wilde A ruffled mind makes a restless pillow. Charlotte Brontë