Don't not ever use heat rocks, as this will result in burns to your snake. if it's a hatchling I'd say a click-clack style enclosure with a heat mat under 1/3 of it so u can have a nice temperature gradient, or u can use a heat cord but what ever u decide please use a good quality thermostat.
If it's an adult I'd say a 6ft enclosure being the minimum, u can always go bigger if u want, heat lamps with cages (is a must) is your best bet for heating then.