There is no hard and fast rules regarding the location of each item of equipment, but normally the engine room consists of several levels having different machinery such as auxiliary engines or diesel generators, a boiler, the inert gas plant, fresh water generator, and purifiers, fuel and oil pumps and storage tanks, the engine control room, waste incinerator, and several other common paraphernalia like electrical panels at various levels.
The engine control room is the command center of the engine room and is usually the only air-conditioned place within the engine room, which is otherwise full of noise and heat. This is because of the presence of computers and delicate controls. Of course, it also depends on the area in which the ship is sailing. In very cold regions, the engine room is cold rather than hot.
I must also add here that apart from the location of the machinery, the location of the engine room itself isn't fixed for all types of ships. Most ships have engine room at the aft, while there are other variations in which it is located either midships or at the front side of the ship.