If you are going to build a custom pitch for your favorite Blood Bowl team sometimes you change the scale on the field to make it easier to play with your big guys. Making the squares a little larger makes it easier to get players in those tight areas and allows more space for prone players without losing track of their position from a slight bump. If you increase the size of the squares you also have to make a customer pass ruler to keep the game run vs throwing balanced. I have noticed people have a problem with this so here is what you do since math is not everyones strong suit.
The width of the whole ruler is 1.695 squares so if you scale to a 40 mm pitch squares gives a 67.8 mm width(40 mm* 1.695). The length of the thrower area is .87 squares so scaled to 40 mm is 34.8 mm.
The Quick Pass, Short Pass, and Long Pass sections are all 3.49 squares so 139.45 mm for the 40 mm pitch. The Long Bomb is actually a little shorter at 2.75 squares so a 110 mm for a 40 mm scaled pitch.
All of my numbers are for a 40 mm pitch. If you are building something like a 30 mm one then just multiple all the numbers by .75 (30/40).
All these numbers are pretty close and should serve you well in almost all games on your new larger pitch.