I really like this idea, but I've never tried it. The big problem with rolling hit points is that, by RAW, you never really do so enough times for the law of averages to kick in until you get to very high levels. If you do it this way, you've rolled more dice for hit points by 6th level than you would in a RAW 1-20 campaign.At Level Up: Reroll all your accumulated Hit Dice. If the total is greater than your current (prior to level up) hit points, you have the new hit points. Otherwise, you keep your prior total.