Dressing Up My Ugly Pole Building

[metalspinner]

This is my first post in this board. Though I have always enjoyed reading along with you guys, the scale of the work can be intimidating. So maybe this little project I have in mind will get my feet wet and give me some confidence?

Here is the front of my workshop...




I'm thinking about adding a timber framed awning all the way across topped with a sheet metal roof. 
Here is a quick attempt to draw what is in my head. 




And a not so good front view 
  



When I'm in the creative mode of designing a piece of furniture, I just lay out the pieces until they look good then measure, mark, and start cutting. Because of the scale of this, I thought I should be a bit more formal in my approach and run it by the experts.  :D :D
Should I cut housed M&T? Is that overkill?
I have ERC logs and can cut 6x6's. Is this a beefy enough look for the size of the building?
The purlins spanning the garage door will be more than 12'. Are 2x4's on edge and dadoed into the 6x6 enough to hold up to sagging?

If you made it this far in this post, thanks! I hope you didn't laugh too hard at my drawing skills. 😂😂

[Don P]

I threw 300 lbs at the load on the purlins. 2x4's on a 13' span are probably going to sag excessively. I'm looking better at 3x4.5" in something at least as strong and stiff as white pine. Housing hides angle changes in the timbers as they shrink and provides a bit more bearing surface, it also provides another place to collect water. ERC doesn't move much and your load is light so your call.

With that slab out front already you really should just put a line of posts on each side of that drive and put a full length entry roof over it. Deep down you know you need more room  :D.

[metalspinner]

Thanks, Don P
I can bump those pieces up in size I think. Might need to hunt down a couple more cedars. 

I'm wondering about the M&T  size, too? 1" x 2" maybe?

[Don P]

I'd go 1.5x4 myself. Typically a 6x mortise is 1.5" wide, an 8x uses 2" thick tenons. You want enough relish beyond the peg on a tenon to avoid a shear failure if there is an uplift in this case and enough wood on the edge of the mortise to peg to avoid a tearout. Cedar is good vertically but is not the best beam material, choose carefully.