My first RC flight video, shot with a phone, (potato) and my first attempt at a stepped wing delta using Dollar Tree type foam board. This is often called Art Board here in the UK.
With a 60% size increase the shape copied from Dutch RC Adventures    • Easy Flying Wing  How to build  
I wanted to use a full width A1 foam board for half the wing span.
Here's a link that he gave for his wing http://fwcg.3dzone.dk/?wing_span=100&...
You just have to size the step as a percentage of the inner and outer wing chord.

This thing flew very easily and was very docile. I had limited the control throws to approximately 50% at the transmitter, but it needs more. I also have built in mechanical differential, so they give less down and more up.
The chord of the elevons (or ailevators if you prefer) is 3 times wider at the outer end. I've done quite a lot of research about RC flying wings and the KF airfoils, and this seems to be the final best choice.
There is almost no stall during flight and if it's level at that point, it just kind of washes downwards a bit and you can recover easily if you have a bit of height, no problem. Even just 20ft (6mtrs) is enough.
I reckon this is an ideal beginners plane to fly, though the build is not exactly simple.
I will build another at some time, using lighter foam as this weighs 1.3 kilos without the battery! Hopefully I will remember to do a build vid too.
Motor mount is made from 3mm liteply. One piece on top and one on the bottom of the central trailing edge double thickness with a liteply 'key' pushed through the top one. They are separated by a couple of pieces of foam to match the wing. And as you can see, the motor mount is on the top piece. The whole thing just slides over the center part of the wing and locks in place with the key going into a 3mm slot cut in the foam. The key is retained with a cut off zip tie.
And the whole thing will fold in half, if necessary .