With approximately 100 people in the ROPD and another 100 people in the City Hall departments, the building would need to be approximately 65,000 to 75,000 square feet.
Given the limitations of horizontal space on city-owned sites without taking up too much parking, a combined building would have to be vertical and a minimum 4 to 5 stories tall. Due to the requirements of separating public and police activities, for security reasons, this type of building would require additional square footage and have multiple stairwells and elevators above and beyond what would be required by code, adding significant cost of the project. This is why two separate buildings types are being proposed for the city of Royal Oak. All the operation efficiencies the city is hoping to achieve will be lost if it starts adding levels.
A combined location works much better in a rural environment where land is available and you can go horizontal instead of vertical.