It is available, but as you do not set it, it has a default value that is NIL.
May be you can try something like:
Procedure do_me (myH : HANDLE);
BEGIN
h := myH;
TheUnitNumber := GetRField(h,'VG-Area Poly','unitnumber');
ForEachObject(process_storage,((NOTINDLVP & NOTINREFDLVP & (R IN ['VG-Area Poly']) & ('VG-Area Poly'.'polyclass'='Area-Storage'))));
ForEachObject(process_balcony,((NOTINDLVP & NOTINREFDLVP & (R IN ['VG-Area Poly']) & ('VG-Area Poly'.'polyclass'='Area-Balcony Open'))));
END;