EDIT: Now I see you're talking T-tail, not conventional tail... Well, I leave my post anyway.


Meassure the distance to the wingtips from the stab LE tips and make sure it's exactly the same distance.

For the horizontal balance of the stab, mount wing, attach stab and walk away from the plane.
When you have some distance to view from it's pretty easy to see if the stab is horizontal to the wing.

For fin, use a carpenters 90degree square and meassure from the (now glued) stabilizer.



...I'm pretty new at this, but this is how I do it.
I'm sure more experienced builders can help you more.