The plugin I use to get pieces on a flat plane is called "flattery." It works well, but you can also do it by hand, if you group each face separately. Takes more work, and more familiarity with SU interface.
I'd leave the dimensions out, until you have the pieces separated, flattened and laid out. In the 3D model, all the extra lines get in the way. Your "person" gives enough sense of scale for me to understand without knowing exact dimensions. BTW, you can get decent 2D and 3D people from SU warehouse for free--easier (and look more realistic) than making your own. See this thread (my MYOG tent project) for example: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=47007.
Once I have a design I'm sorta okay with, I copy it a few feet away and make changes to the copy, so that eventually I have a whole line of variations, all in the same file. Learn to use layers, components and groups, if you haven't already--they'll save you a lot of time. And SU's "sticky" geometry (the way tugging a corner or edge of a face changes the shape of attached faces) is a really powerful tool for tent design, but takes some practice.
Regarding your design: to my eye, there's elements that can be simplified, including number of poles and number of seams. It feels somewhat "overbuilt" (ie, heavier than necessary). Take advantage of SU's ability to calculate area ("entity info" under "window" drop down menu). Use tape measure tool to get lengths (and create guidelines). These tools, plus knowing how much your materials weigh by area or length, will let you ballpark final project weights. I'm not sure what the little rectangular openings in the foot and head end of your canopy are.
Looking forward to seeing how it evolves.