Generally, heavy rock = heavy strings. Heavier (or thicker) gauge strings tend to give a fuller more bass-rich sound when played hard and also take the pounding of heavy strumming. The downside is that they're harder on the fingers, especially for beginners, and are more difficult to bent when playing lead. 11 gauge string sets are the most popular for pro Heavy Metal. (See here for discussion of what gauges mean!) Fortunately there are many options for the heavy metal guitarist, with many guitar string brands offering ‘hybrid’ string sets. These are typically heavier strings at the low end (6^th,5^th and 4^th strings) for a driving rhythm sound coupled with lighter strings on the top strings (1^st, 2^nd and 3^rd) to make playing lead easier. Heavier strings are also much better for dropped tuning (aka detuning), with dropped D being the most popular. Here’s some examples of some great heavy metal or hard rock strings, to compare the gauges:

String number	1	2	3	4	5	6
String note*	E	B	G	D	A	E
Guitar String Brand	String gauge / 1,000s of an inch
D'Addario EXL140 XL	10	13	17	30	42	52
Dunlop Zakk Wylde	10	13	17	36	52	60
Ernie Ball Beefy Slinky (Optimal for Drop D tuning)	11	15	22	30	42	54
Ernie Ball Power Slinky	11	14	18	28	38	48
Ernie Ball Heavy Top Skinny Bottom	10	13	17	30	42	52.
Rotosound Roto Blues	10	13	17	30	42	52
Rotosound Roto Reds	11	14	18	28	38	48
GHS Boomers	12	15	24	40	52

*note shown for standard EADGBE tuning.