Im need to make 2 square holes in the garden which will be filled with concrete a post base will then be bolted to it to hold a 8inch oak post ontop. These oak posts will hold up a flat roof over my patio with the other end of the roof coming off the house. Im using the T blade concealed bases My question is how big should the holes be compared to the post bases, i was thinming 12inch would be oak so 2inch over the base each side. Could anyone adviss. Also depth wise, 800 to 1000mm? Thanks