The usual method using the radius of a circle, I just looked at some boxes on the internet found some I liked and decided an 8ft radius would be a good start, sketched it out and it looked great, didn't bother sketching any others.
So what you do is decide on a radius, then use a piece of string or if you want to be accurate use a piece of wood like I did then you nail one end into the ply and put the pen on the other end and it will sketch out a perfect constant curve.
Ive tried like 3 different methods and they never give a nice take off?