Base : the lowest part or edge of something, especially the part on which it rests or is supported.
Roof : the structure forming the upper covering of a building or vehicle.
Height : the measurement of someone or something from head to foot or from base to top.
Top : the highest or uppermost point, part, or surface of something.
Climax : the most intense, exciting, or important point of something; the culmination.
Antonym of Base is Top