Have done construction my entire life but never built a pergola. It's for my mom and she wants it heavy looking. Roughly 10'x12'. 8"x8" treated post in corners only, 8"x8" header. Would like to use 4x6 joist on 24" oc running the 10'. Barge rafter in corners. So joist will go in like a corner hip. Here's the thing. Want to have the ceiling with 4x6 on 24"oc in both directions. Creating 24" boxes. I know that's a lot of weight. Will the 4x6 on 24"oc hold that span plus the extra weight going the other direction.