Get a copy of ICC 400, the Standard on the Design and Construction of Log Structures. Contains design values for graded logs, properties, etc. http://shop.iccsafe.org/icc-400-2017-standard-on-the-design-and-construction-of-log-structures-1.html
Your best bet is to run the king post continuous to the top of the rafters. House, mortise and tenon the ridge beam into the side of the king post, and then mortise and tenon and house the rafters into the king post as needed to "hang" the king post from the rafters. This avoids tension...
Bala0404 said it was to be DRY flood-proofed, not wet flood-proofed. Therefore no water in the structure and net buoyancy if the water level is two feet above the slab.
