how to make bitters

hey man, ok my whole family and friends are convinced of my success with digestive bitters that they now want to try and where wondering if i could make them for cheaper as was myself without the berberine herbs and stim laxatives.

So what herbs would you recommend and do i just buy the raw powders of the herb i take it.

if you know any books or links that will not make me burn the house down or myself that would be appreciated.

Cheers