How to develop building management system?

I am going to develop windows application system using C# and MS sql server.
I want to develop a building rent management system.
for example. if building BG1 has 10 floors(G+10) and inside each floor there may be different number of offices or shops.
Building BG2 has 6 floors(Ground +6) and inside each floor of this building there may be different number of offices.
Now i want to develop windows application software so that one can easyly manage the building rent system.
I will have report systems based on months and years for each floor and tatol reports of occupied offices and uncoppied(available offices).
the system should have a means to add floors and offices.
could help me please how to start this application or if you have any system related to this let me know it please thanks all.
together we can make it simple.