Are you dimensioning the frame alone or the floor plan as a whole? If you are dimensioning the a complete floor plan, I would probably approach it differently than if you are dimensioning the timber frame alone. The drawings are there to relay information, and who the information is for can impact how the information is presents. As they say, know your audience. Either way, consider the modules of the other materials being used. Typically the timber frame is custom cut, so I try to use dimensions that are most efficient with standard sizes of other materials (nearest 8" for concrete block foundation, typical framing spacing, typical SIPs widths, etc.). For me, the written dimensions is not the key, the key how efficient (or inefficient) that size is for the materials being used. I have also found that different contractors like to see the dimensions show different ways. There is no one set "standard", but there are a some ways that are more common than others. Talk to contractors in the area of your project. My experience has been they are usually willing to tell you the things that make there life difficult or what would make drawings easier to build from.