Estimate the number of windows in NYC?

Here is my approach. Please Let me know if this seems reasonable:

1. 1. Assuming - windows for buildings only, do we also want to include windows for cars, buses etc.? 

   2. A window is any form of a glass or fiber panel that allows for light to come in

   3. Assuming NYC is 15 miles long and 4 miles wide -- > 60 square miles

   4. Based on my experience, I have noticed that 40% of NYC is high rises for work or corporate offices. Thus 24 sq mile is occupied by high rises. The rest of the space are buildings for residential purposes. 

   5. Assuming NYC population: 8M users

   6. Windows in NYC = Windows in tall corporate buildings + Windows in residential units

   7. Windows in a tall building:

      1. # of tall buildings * average # of windows per building

      2. The number of tall buildings:

         1. Per mile of walking in NYC, I have seen about 20 buildings

         2. Assuming every building is 50 stories high on average

         3. From my experience in a highrise, a tall corporate building is usually rectangular and surrounded by windows on 4 sides. On average I have seen 50 window panels on each side. 

         4. Thus every floor has 200 windows

         5. # of windows per building 200*50 → 10000

         6. # of high rise corporate buildings

            1. 20 buildings per mile

            2. Thus for 24 sq miles, we have 24*20 → 480 highrises

         7. Thus windows for 480 highrises → 48*10^5 windows ~ 4.8M windows -- (A)

   8. Windows in Residential Units

      1. 8M residents

      2. Assuming 3 residents per household → 8M/3 ~ 2.7M homes

      3. 20% of these are houses, 80% are flats or condo units

      4. 0.5M are houses and 2M are flats

      5. Houses average windows are 15 windows 

      6. Flats average windows 8 windows

      7. 0.5M*15 + (8*2M) → 17M windows -- (B)