Timber frame shed, post and girt reinforcement?

Hello everybody.

I'm starting to make a small timber frame shed, cca. 3×2m (10 by 6.5 feet). The posts will be 15×15cm (6×6 inch). Now, I have decided that the general outline of the building should be something like shown on the sketch.

What I can't decide on, and this I would like you to help me, is what to do with the lower girt. How much should I reinforce it? Will knee braces be enough? As far as I understand, they are there more because of the lateral forces. What about the long diagonal braces (I don't know how this style is called)? It seems to me that they resist the vertical forces a bit more. Or do I just add another post directly under the other?

And about the girt to post joint. Mortise and tenon, lapped dovetail, or something else?

All opinions welcome, tell me what would you do.

Thank you for the help in advance.

Edit: I made a mistake on the sketch, the girt seats on top of the beam, not the other way around like on the sketch.

Hey,
I am by no means an expert in timber framing, but I would have another post in under your horizontal one where it meets your upright next to the guy in your sketch. And would put some kind of cross bracing in. It probably doesn't matter that much on a shed that small how you do your cross bracing but it should probably have some at least. Just my opinion.

Hi- I've designed and built a lot of frames in the last 25 years. Considering that this is a very, very small frame, and you're using 6x6 timbers, I don't think you have too much to worry about. Wood species will determine the size of your timbers. Stronger species like Oak will carry more weight, weaker species like Pine will carry less weight and need larger timbers to accomplish the same thing. An unusually large dead load like a slate roof is another concern. In that case I'd consider beefing up the timbers to 8x8, or even 8x10 on the 10foot spans, and adding 2foot braces at several points (under the 10foot spans). Otherwise... good to go.