I agree, do not use Siemens or Notifier or Simplex. Those are a complete waste of money for a four story building (IMO)
As long as you don't need more than 512 (i know there is the system protocol, but its not my choice) initiating devices, get a silent knight 5820XL. (firelite is fine, but I don't personally find it user friendly)
Better yet look for a silent knight dealer which is called an Engineered Systems distributor.(ESD) Typically they will work with you, supplying the panel and devices and you and your team installing. They will do the programming as well, are not as expensive and you can changes ESD's. Allowing you to deal with the same product, different dealer. They can do many more initiating devices than 512. Your size building does not require a propriatary system.
Please plan plan plan.
Oh and sell nonPOTS communications. Analog Phone lines are going away eventually. There is a primary cell only communicator (DSC GS-305ICF). And also primary Internet communicator (firelite IP-DACT). There is also AES radios, but not everywhere.