I am wanting to build a pergola over my existing patio I would like to catch the early morning sun in the east and as the day matures have the western afternoon sun blocked causing the patio to be shaded.  I am currently considering a 22-degree angle open to the East which hopefully means that by 2-3 P.M. my patio would be completely in the shade.

How would I keep those angled timbers from bowing over time?

thanks for your responses

Orvals