PJ im planning on building one of these when we get our new place, I really like the idea of making a power rack out of wood cause a) I have shit welding skills and b) As noted they are more quiet than a steel rack. I have moderate skills in woodworking but you would only need basic to no skills to build this if you think things through and go slow.
Edit:
@Leigh to calculate the maximum weight your DIY power rack can handle do you guestimate the weakest point and test its strength somehow before building it or the point with the heaviest load and test its strength? Id imagine the latter would be the back end of the rack where you rack the bar when squatting.
Im pretty sure I can build one that can handle more than 500LBs using Aussie Ironwood, not sure how to calculate it though. I found the janka test but its for hardness.