Here is an Octagon Picnic table I designed. If you would like all the dimension and materials needed to make one too here's a link.
https://www.etsy.com/LastLeafStudioSh...

Amazon Links :
Predrill + Countersink bit - https://amzn.to/3tLVE4v
Circular Saw - https://amzn.to/3toyVv7
Deck Screws - https://amzn.to/3NzZeGF
Miter Saw - https://amzn.to/3tqqf7f