Ambience tracks are not usually mixed very high on a typical metal mix. That doesn't mean you should ignore them. Besides the obvious room sound, good ambience tracks can add "glue" to the drum sound. If you are recording in a very good room, they can make the drum sound very three-dimensional. They can help to bring back the "whole kit image" you lose with the overheads.

You want the ambience mics to capture the room and the kit. Try to find a spot in the room with your ears where both of these qualities match. The snare is the most important element of the kit. Listen to it carefully. Again, cymbals are your enemy. What you really want to hear are the drums, not the cymbals. You can hang some blankets around the drums using microphone stands to help this.

Ribbon microphones work great in capturing the drum ambience. Most of them have a bi-directional polar pattern. By using two ribbons in a Blumlein configuration (two bi-directional mics crossed at 90 degrees), you will get 360 degrees of room sound! The cheap t.Bone/Apex/Nady ribbon microphones are just fine. Ribbon microphones also have a darker sound, which can help with controlling the high end.

If you have to place the microphones very close to the kit, try to follow the "center line" of the kick and snare drum. You will get less phase problems and a better stereo image.

If you don't have any ribbon microphones, experiment with different condensers and dynamics in stereo or mono configurations, aimed at the wall, ceiling or floor. Place them behind the door or in the corridor. Even inside the trashcan! Mic the wall with a kick drum mic! Do what ever it takes to make it good. Go crazy!