This is what the manual says about creating your own patterns:
Using BR-800 Rhythm Editor
By using “BR-800 Rhythm Editor” you can create
your own original patterns, arrangements, and drum
kits using a computer.
“BR-800 Rhythm Editor” is provided on the “BR-800
DVD-ROM.” For details on where to find “BR-800
Rhythm Editor,” refer to “ReadmeEN.txt” on the
* You won’t be able to create patterns or drum kits
using just the BR-800.
* You must install the USB driver before you connect
the BR-800 to your computer (p. 118).