I tried to make make some cube shaped pumpkins last year but I built the box too large and it never really worked out . I've recut the box again this year using last years box and I got to my pumpkin a lot sooner. It's already developed flat spots on all 6 sides and I'm hoping it will grow out into the corners of the box soon too. It'll add to our now 'freakish' collection of garden plants such as our 9ft tall sunflower and it's (now) 14 headed, 8ft tall neighbour, and our marrow sized courgettes.