Quad+ Fan Radiators
The size of your radiator depends on the space inside your case. most higher end cases have room for a watercooling radiator.
Radiators are categorized into how many fans you can fit to them. This is usually an indication of how it would fit inside your case. A radiator size is determined by its fan size then the quantity of fans per face, so a triple 120 radiator that fits 3 fans would be a 360mm radiator some specialist radiators are available in 140mm fan sizes but are usually more difficult to fit into a case so watch out for that.
The more you have to cool, the more radiators you will need.