A glass roof is a common misnomer for Skylights.  Some people probably think of it as a sun roof in a car too.  To us, any nice skylight overhead could be considered a small glass roof.  Actually, many skylights,  particularly the older ones are plastic dome skylights rather than glass (we rarely recommend them).  We almost always recommend glass these days for anything that goes on the roof because the glass is so much more energy efficient.  Technology has taken great strides in glass sealed units that are used for skylights and windows. Today they come with Low-E coatings and argon gas, between the two glass layers.

In fact, the Velux brand of skylights has recently raised the bar a little higher (again).  In 2014, they have introduced the new Clean Energy Plus Glass that is another step further in energy efficiency and convenience.  This new glass is triple coated with Low-E, dual sealed and injected with argon gas.  It has an extra thick laminated interior pane, designed for safety and energy efficiency and offers three times more protection against solar heat gain.  And for ultimate convenience, the exterior pane has a new Neat coating; this smoother surface disperses water evenly, removing dirt more quickly and reducing water spots. 

Cuz who wants to climb their roof to clean their skylight!