Building a better bankroll

I cashed out last month at every site i could. Now I am starting over. Lower limits climbing that mountain again. What is everybodys theory of min to keep in the roll so cashing out is not such a set back. I think in the future i will not cash till i reach milestones and then only a third of the roll.

There is such a difference in play in the different levels that what I have done doesnot work so well.