a method for erecting a drilling rig and an apparatus therefor having a mast , a base , a floor support , legs arranged between the base and the floor support , a primary lifting ram in engagement with the mast , and a floor support lifting ram , is disclosed . the method involves raising the mast with the primary lifting ram , raising the floor support with the floor support lifting ram to an intermediate height , engaging the primary lifting ram with the floor support and raising the floor support from the intermediate height to full working height with the mast lifting ram .