Made this real quick to insert the area of an object. should give you a starting point.
(defun C:Obj_Area (/ ent objid pt hgt str)
(vl-load-com)
(setq ent (entsel "\nSelect Object"))
(setq objid (vla-get-ObjectId (vlax-ename->vla-object (car ent))))
(setq pt (getpoint "\nSelect Point"))
(setq hgt 0.250)
(setq str (strcat "%<\\AcObjProp Object(%<\\_ObjId " (itoa objid) ">%).Area>%"))
(entmake (list (cons 0 "TEXT")
(cons 10 pt)
(cons 40 hgt)
(cons 1 str)
)
)
(princ)
)