It appears that no one has found a pattern for this design. It is my opinion that it is Amish designed. It looks typical and again my opinion there is no pattern available as they are kept rather close to home since the qultmaker is probably noted for the specific design.
So, my best advice is you need to graft the pattern out in order to duplicate it. You an start with a commercial pattern showing sizes of the center such as Eleanor Burns book but from then on you need to determine the sizes. But when you do, work in even inch incriments which will be much easier. You an get wide graft paper at a Blueprint Shop or art supplhy shop. It comes in 42" width. Work on the square corners to get them the size you need and then add small borders between that part and the center if you need to fill in for fit. A classic design story silimar is when Jinny Byer designed Ray of Light back in the 80's she did the center and then the border and they did'nt fit so she just added some narrow strips between the two until they did fit.