I don't know about 10% but I'm planning on make a root beer (Like an actual Root - Beer) at whatever strength, maybe 4-5%.
I haven't fully flushed it out, but if I can get the ingredients, I want to try something like steeping (but not boiling) a tea out of burdock root, sassafras root bark, sasparilla root, dandelion root, and maybe wintergreen leaves.
Then boil up a wort with some light DME and maybe some darker steeped crystal for color and a bit of flavor, maybe some hops maybe not, some vanilla extract, cloves, nutmeg, cinammon sticks, pound or two of brown sugar or molasses, add the steeped tea after the boil is over.
Then I plan to use, I'm thinking... Belgium Saison yeast. Besides the spicy peppery flavor profile, it's a very warmblooded and finicky, notoriously prone to sticking or slowing greatly after like 1.020 or 1.030 gravity, so lots and lots of residual sugar. Cause root beer should be sweet.
Then taste, maybe add more sugars to taste, or not, maybe allow it to slowly ferment a bit further, and then bottle. With 1 plastic bottle in the batch, to squeeze and test for carbonation, and wait for the saison to either kick back in from aeration or take it's sweet time (true to form) at warmer temps as needed, whichever.
When it's carbed, I'll not just fridge but freezer crash it to as near freezing I can get without bottle breakage (getting a bit slushy perhaps, like you might do with pilsners in the summer?) and then refridgerate it forevermore. The low temps and quicker cool off should shock the damn hot-blooded Saison into a nice coma if it doesn't kill it outright. And even if it doesn't, I doubt the yeast will do anything at fridge temp, since most people need to ramp the temp on it up to as much as 90 to get the strain to finish from what I read.
I'm very optimistic that if I at least keep it in the fridge I won't get bottle bombs, but who knows.
If not... drink faster.