People who live in flats are usually unable to enjoy a barbeque in their home due to the lack of open space available.
For most flats, the only exposure to open space is through the windows. Some people currently utilise this by, for example, drying their clothes. They do this by putting their clothes on a long metal pole or rack, and then hooking this out of their window. This is a surprisingly effective method for people in flats to dry their clothes outdoors, and has been used for decades.
A similar method could be utilised to provide barbeques to flat dwellers, although there are a lot more safety precautions that need to be accounted for. Giving a barbeque the ability to be hooked onto windows could mean that there is sufficient ventilation for the fumes and heat to escape. However there are still many problems with this solution, such as the prevention of fires around the barbeque, and also the prevention of hot items dropping onto the streets below. It will also have to be able to fit onto different types of windows and frames with sufficient strength.
As always if you think you have a solution or if you have a problem you would like me to try to solve then please feel free to comment it.