Leak or condensation

[Stotty1]

Hi
Last summer we had a single storey extension with a vaulted roof built. The extension is divided into 2 rooms with a Velux in both.

During the snow before Christmas when we had the snow, we noticed a wet patch to the right of both Velux windows, strangely in almost identical places in both rooms.

,

The builder said it was due to the snow and has put some leading on the tiles around the widows.

It dried up once the snow melted and all was good until this last week.
The wet patches have came back this week but they seem to come and go. They are normally there in the evening and gone by the morning. I'm starting to think is this due to the extra heat in the room in the evenings.

Has anyone got any ideas of what could be causing it and how we can stop it?

They are not the best but I will add some more photos I took of the roof during the build.
Thanks

 

[Wayners]

Fix some plastic over.
If water is under it's a leak.
If water is on the plastic surface its condensation

 

[robinbanks]

Looks like it's coincidental with the joint between the plasterboards.. Water dripping onto the back of a plasterboard tends to show through at the edges first

 

[Stotty1]

This morning for the first time it has appeared on the other side of the window.

My thinking is it's condensating in the roof space and dripping then running along the insulation until it finds a way out, which as you say @robinbanks is the edge of the plasterboard.
Also with it being north facing, there is frost on the tiles almost all winter which I guess doesn't help.

If this is the case I have no idea how to stop it, it does have a breathable membrane in place.
The builder reckons there must be a cracked tile but I have looked and can't see one.

Any ideas of what to do next will be greatly appreciated.
Thanks