[Kiki]

Hi
I have a 6 x 4 poly carb greenhouse with no window or other vent bar the door. I need to increase the ventilation and thought I could buy spare parts to make one or 2 roof windows. A few minutes google searching has found nothing. Anyone done this bit of DIY and can advise?
Or would it be better to install 2 solar fans to opposing panes instead?
Any thoughts welcome.

[8doubles]

I would have thought that the apex* of the wall opposite the door would be the place to put a vent or just leave a section out during summer.

*pointy bit at the top 

I have made a 'hit and miss' vent  by drilling several 30mm holes in 6mm polycarb in the door.
Handy for windy days when you need ventilation but not enough to cause damage.

[mumofstig]

I would have thought that the apex* of the wall opposite the door would be the place to put a vent or just leave a section out during summer.

That's exactly what I do, remove the top pointy pane of glass