A ballpark figure would be fine.
Since we are on Mars, I would suggest making a two part building, one to protect the high pressure parts from dust, but remain rather unpressurized (which means less heat loss), the low pressure gear and the control center would be better placed into a pressurized structure.
So, the height of the high pressure part building is defined by turbine system, condenser and deaerator, all three stacked on top of each other. Means in your scale of things, already about 15-18 meters, plus some space above the turbine for a maintenance crane. The biggest part is likely the condenser, with about 4 meters diameter, so you need about 6-8 meters above the machinery for a portal crane.
Since you have two cooling towers, this part of the building should contain 2 turbines, each giving you a 20 x 30 meter footprint on Earth, better add some space more for having people working in a pressure suit. So the unpressurized part of the building would be 50 meters wide, 50 meters long and 25 meters high and have the appearance of a fireworks factory (strong walls, weak roof). At the end away from the reactor, you would have a low bay hall, that can be reached by the portal crane and has large doors on both sides that permit bringing new machines into the building.
Next to this you would have a pressurized low pressure machinery part. This part of the building should be pressurized for easier working, also it would contain many smaller control systems and pumps, that are easier cooled by one central ECLSS (Mars!). A series of cylindrical tanks in a common concrete hull would be one good estimate of the building structure, parts of this building could also be hidden below Mars soil, it needs not much beauty. A window is not needed in a place, that humans rarely visit. I would not put it underground and below the turbine systems. Better have it be between the low bay part of the turbine building and the turbine hall, so you can have an airlock there.
I would say, giving the main turbine building two lower building wings in the middle, each 6 meters high, 20 meters long and 10 meters wide should do it, and have contact with the pipes that run to the cooling towers, since you would control the main pumps and valves from inside it and distance is expensive.
Finally, you should have a low section of unpressurized, dust protected space away from the reactor, with the electrical power distribution systems. make it 30 m wide, 15 meters long and 12 meters high, that should do it. Have about 10 meters distance between low bay of the turbine building and this hall, since such high energy electrics like to get out of control sometimes and cause nasty fires, even without oxygen.
So, all together two blocky buildings, with the bigger having two side wings.
