Ah, so the basic QAYG block.
The second pic is another option but certainly not as easy as the first one.
If you're going for the first method, make the rectangle any size you want. The one I used have proportions of h=2xwidth.
But it really doesn't matter, as long as the strips are placed on an angle.
I would start the block in the middle so you know you've got the correct angle.
Then work both sides. Same points I wrote above...make it oversized so you can trim it down.
That way you don't have to worry about everything fitting perfectly while you're sewing on the strips.
I hope that makes sense and answers your questions.
QAYG is a very versatile technique and you could have a lot of fun with different shapes.
Just something to keep in mind for a future project.