Advanced chords

Im wondering how to fit cool chords into my play. Metallica always throught in cool sus2s or maj7s n that. Im wondering how you then work out the scale you can use to solo over.
Should I learn the composition of these chords. Ie Major = 1,3,5. Minor 1, em... 5.

Should I put a big chart on my wall!?

Well, this is just a suggestion . . . Make a chart (I suppose it could be big) that shows the key of C major and all its notes across the fingerboard.

Now Asus2 is nothing but an A chord with a B stuck in instead of the third. Look up on your chart, and you'll see how this fits into the key of C. Do the same thing for Cmaj7. Cmaj7 is just a C chord with a B. See how it fits?

Do the same thing for tons of different chords and keys.

This is similar to what Christoph said, but I used to do it a lot. Learn your scales, then learn about chord formulas. Once you do that, start putting different scale degrees into differend chordes and see what voicings you get. It'll get you really familiar with how different chordes sound, and since you getting familair with the notes that compose chordes, you'll have a better idea of what notes to use when improvising over them.