The Rubies help to automate some aspects of the design... you'll still need to have a good handle on drawing in the program, and using components to create 'timbers'. The vast majority of your modeling will be straightforward SketchUp use.

After you build up the model using components, you'll be able to use the TF Ruby to create a timber list (you already have your material, so you won't need this). Then, when you feel like you have a mastery of moving, copying, rotating, precisely aligning parts in relation to one another, etc., you can begin creating joinery and adding it to the already created timber components. The joinery bits are just additional components that live inside the timber components, and the Ruby scripts are behind the scenes data that tells SketchUp how to handle certain elements - for example - peg counts or creating the mortise and housing when using the shop drawing Ruby.

Clark may have a different opinion, but if you have little experience with SketchUp or other 3d modeling programs - I'd work on the basics first, and add the Rubies as you aquire skills.

And you'll likely be able to cut that frame just fine no matter where you are on the 3d modeling learning curve...