I don't think "maate" itself is declinable. It's a bit strange actually, because "enaa maate" sounds fine and so does "enii maate", but "enu maate" which would be neuter does not sound right.
If you just remember this, that "enaa maate" means "for that/for him" and is used for masculine nouns, and "enii maate" means "for her" and feminine nouns, you should be ok :s.
Also, if it used to mean "in order to", then there will only be a verb ending in "-vaa" before "maate", and no "-nii/-naa". Examples:
karvaa maate = (in order) to do
lakhvaa maate = (in order) to write
ley javaa maate = (in order) to take away