The rules for rolling your own seed phrase:

- Get 2 x 20 sided dice and 2 x 10 sided dice.

- Make sure they're different colours so you can distinguish between them.

- One of the 20 sided dice (the indicator dice - brown in my photo) is used to decide if the number generated will be 1-99. If it rolls a 1, you disregard the number on the other 20 sided dice.

- Roll the dice 12 times to get your numbers

- Convert the numbers to the words on the bip39 word list.

- The last word (the checksum) probably won't be right so you will need to try the other words in the 16 word section in the list to see which one works. You can do this on your hww so the process remains completely offline.

- You'll want to use each dice for only one part of generating the number to remove human bias. In using the brown for the indicator, the blue 20 sided dice for the first thousands and hundreds column, the blue 10 sided dice for the tens column, and the red for the units.