The pergola will be built from redwood and will cover an area of 20' X 16'. There will be 3 posts on each of the long sides, measuring 6"X6". I plan on sandwiching those posts with two 2"X10" boards and then putting on 2"X8" rafters across the 16' span.

Does this sound like it would work? My concern is that the 16' rafters will sag. I can have the posts span a 12' distance and then cantileaver the otehr 2' on each side, is this needed?

Thanks for the help in advance!

So, your longest unsupported span will be 12' with 2 x 8 lumber.

What is your on-center plan for the rafters? You don't need to worry about snow load in your climate (just wind)and the span chart I looked at indicates with 16" centers, using 2 x 8 lumber, you can span approximately 23'; and on 24" centers, 21 feet.

From the linked photos you can see our pergola. The posts are on 8' x 12' centers with a 2' overhang on the corners. All lumber is 2 x 12 but with the rafters "nested", each is in effect, 2 x 6 though I have a lag screw at each intersection to tie the members together. No problem after 5 years and I reside in a snow zone.

Plan to install footings for the posts before building the paver patio. Hope this information helps. Good luck.