Sunbrella is awfully heavy for an awning that size. I would go with something lighter, like Stamoid. You should also consider scalloped sides to get better tension. Taking down an awning during a squall at 2AM is no fun, so build it well enough to stay up. Sailrite
has a video on making structural awnings with scalloped sides.
Last thought: Consider soft attachment points like webbing loops instead of metal rings and grommets. If you do have to take it down in a breeze, you do not want half an acre of awning flapping around on deck
with lots of metal sewn into it.