This might be a duplicate question, but since as far as I know beer uses fermentation and no distillation, I expect the maximum alcohol level to be around the same maximum as for wine, which I believe is somewhere around the 13% to 15% level (by volume) as this is the level around which micro organisms seem to die.
I know some beers in the 10% to 12% range, like the Dutch het Kanon ("the canon") by Grolsch at 11.6% and Grand Prestige by Hertog Jan at 10%, both of which I like. They have a bit of a sweet caramel-like flavour, but I'm not sure if that related to the amount of alcohol in any way.