Tailplane area is generally in the region of 10-20% of the wing area, whilst the aspect ratio (spanē/area) is usually in the region of 2/3 of the AR of the wing.
Of that tailplane area, I'd expect to see that the area of the elevator is around 15-25% of the total surface area of the tailplane.
However, this is a gross simplification, as is what follows, but nonetheless works far better than intuition says it should:-
(1) Draw out your aircraft planform on thick, stiff, cardboard. Leave the tailplane a bit oversize.
(2) Cut around the planform, balance this on the edge of a ruler which is aligned spanwise.
(3) Trim down the tailplane until you get a balance point roughly 82% of the mean chord behind the leading edge.
As I said, this works better than it has any right to, BUT there's no substitute for then working through a theoretical estimate of static margins using the standard formulae which you'll find in texts like Stinton or Raymer. The bigger a difference there is between the aerofoil sections used in the mainplane and tailplane, the more critical these calculations become - I recall one type where some blithering idiot of a company designer had taken a perfectly good (okay, slightly marginal) design with a large inverse camber on the tailplane, and for reasons best known to himself substituted a symmetrical section - leaving virtually neutral stick-fixed AND stick free apparent LSS.
For references, try
Houghton,
Stinton,
Stinton,
Raymer