G'day

I am planning to make a small bench style seat and need some advise regarding the design and what joints to use

This is just a rough not to scale sketchup of what I am thinking

https://docs.google.com/open?id=0B7t...XZ0dEExMm9JYXM

I like the idea of keyed tenon on the bracing wood because I like the looks of it and also it is something I have not done before.

What I am not sure about is how to attach the top, I don't like the idea of using metal brackets would prefer to use just some wood joints, also do I have to consider wood movement like you would a table top?

Here is a picture of the timber slab that inspired the project that I picked up at a market. I would like to keep the nature edges.

https://docs.google.com/open?id=0B7t...E1uX09oRUxlSXc

The guy I bought it from said when he bought it he was told it was blackbutt but he wasn't so sure of that as he thought it looked more like yellow stringybark, if there are any experts out there that could shed some light that would be great.

Any comments, suggestions, criticism would be appreciated.

Thanks,

Flash