First figure out what key the solo is in. If its in a major key, the chords are
I ii iii IV V vi viidim.
If its in a minor key the chords are the same but they start from the 6th, so
i iidim III iv v VI VII
Upper case numeral means major, lower means minor, dim means diminished. The numerals represent the tones of the scale, so in A, A is I, B is II, and so on. If it is I it means that the first tone in the scale can have a major chord built from it. If it is i it means the first tone in the scale has a minor chord built from it. Am I making any sense?