Any suggestions for a small flat roof window on top a small bathroom extention?

[redfish]

I plan to build (or have built) a small guest bathroom extention within a lightwell of a residential block.  The internal dimmensions of the bathroom are small at 2m x 1.05m.  The sole external wall of this new bathroom faces the dining room and kitchen, and I would prefer not to place a window on that external wall, as anyone in the dining area or kitchen would see that the bathroom is being used (with or without frosty film), and I am thinking of placing a window on the flat roof, but I want it to small enough so that a person cannot enter the bathroom from the flat roof.  

 

Many of the flat roof windows I have seen are large (i.e. inernal dimmensions of 50+cm) to provide access to the roof.  This is not important to me as access to the roof for maintenance can be done via other means.