[joyfull]

Yes drill some holes high up and if you can staple mesh over them and yes add another perch (they may still squash on one but best to be prepared) 

[Casey76]

Is the window in the door made of weldmesh?  If yes, then this will be more than enough ventilation - in fact I would probably try to cover the bottom two holes up so that the holes are aboue hen height

[joyfull]

this type generally have perspex as the windows.

[Casey76]

Wow that's posh!  'Round here it is just weldmesh!

[Pepperpincushion]

Yes, its perspex. I had thought about replacing it with mesh, but I thought the holes would be TOO big.

[jinty1911]

It's very similar to mine but my windows were empty (What's the door for anyway?).  I have covered the window with a piece of black water-proof matting and drilled 3 ventillation holes on other side of the house up above the perches, so the girls aren't in a draft.  Am pleased with it at the moment, although my chicks are out in the garden most of the day as my run is too small.