Western red cedar design values can be found in the WWPA grading rules handbook, and they are listed in the Guild Timber Frame Joinery & Design Workbook (available through this web site). The wood is just over half the strength of Doug Fir and is not suitable for tension joinery or significant bending loads.

We have worked with western red on several outdoor projects. It's weak, hard to work and damages very easily when handled rough. Maybe it's cheap for a reason?

The other problem you will have is attempting to work with 6x6's for posts. Not much room for joinery. You would be best to move up to 6x8 at least for those members.

Good luck and do your homework.