I'm modeling a TF house design with Sketchup. I'm not a pro, just a DIY'er trying to design what I want to build. It's not a simple frame, the building is Z-shaped with an attached garage, so four sections perpendicular to one another. I'm working on perhaps the 15th iteration of the design, 'cuz the more I do the more I learn... I'll realize I've drawn something fundamentally wrong, and it's easier to start over than move 300 or more components around.

That said, I've got (many) questions about drawing construction models with Sketchup; some cover basic aspects, such as: if I'm drawing 8x8 timbers, and we all know 8x8 timbers don't really measure 8" x 8", should I be drawing them as 7.5" x 7.5"?

Beyond the basics, I've run into a challenge specific to TF design. I'm confused about how to join two perpendicular roof sections, at the plates where they share a post. Each of the bottom plates should be on top of the post, and the top plates (forming the roofline) intersect there, too. This pic shows what I mean:


I've studied other drawings of L-, T- and cross-shaped TF buildings. In some cases the perpendicular sections of the building are different widths, allowing the top plates of the wider section to attach lower on the shared post, or to a lower beam instead of the bottom plate. In other examples a perpendicular section's wall is offset a bit, joined to the other section by a short beam and another post, providing separate locations to attach the roof plates.

Neither of those options are optimal for the building I'm designing; these two perpendicular sections are the same width, and the walls are on the same plane (as currently designed). If I need to, I could redesign with offset-walls, but I'm hoping there's an easier solution.

And finally, due to ignorance I'm drawing the entire frame using 8x8's; I'm not an engineer, have very little idea how to properly size timbers. We live in Southeast Alaska, so there's some snow to worry about... it's usually wet and heavy. At present I've drawn the entire design with butt joints, no joinery is modeled yet. I do have the Timber Frame Extensions (TF Rubies) installed; I plan to draw the joinery later, after I've completed the overall design.

Thanks for any help...