Support legs should be fixed hanging down into the tank to support the roof when the tank is empty. These legs should be retractable to avoid diseconomies in relation to the volume of the tank. To avoid sinking due to rain water, a system should be fixed to drain the rainwater. This could be done through having a sump set in the low point of the deck which is drained through a flexible pipe work. An anti-rotation device should be fixed to prevent the roof from rotation. Also, a rolling ladder is fixed to provide access to the tank. Between the rim and the floating roof, a fire detection system should be installed to prevent fires. Firefighting equipment, usually a foam dam, should also be fixed.
There are three types of floating roofs which can be installed: external, internal and closed floating roofs. The external floating roof should be fixed floating on the surface of the liquid product such that it rises or falls depending on the product level. The internal floating roof is fixed to provide protection of the floating roof from other elements e.g. lightning. A tank vapor space should be left above the floating roof and below the fixed roof to allow for natural ventilation. A closed floating roof tank is similar to an internal floating roof tank but in this case the tank vapor space is replaced with a pressure vacuum vent. The best material to use for floating roofs is aluminum since it is corrosion- resistant, high strength and light weight.
Google is your friend : https://www.google.com/search?q=floating+roofs&tbm=isch
can we get some visuals?