Attached to the end of our house is a small shed. It has four (newly built) brick walls and a bitumen corrugated sheet roof. The shed was finished about eight months ago and is fairly waterproof. However, in the last few months we've noticed, what I presume, is mould on the inside of the roof. Although it appears dry to touch, all our belongings are covered in drops of brown liquid (from the roof).
Could the mould be caused by a lack of ventilation or is there another plausible reason? BTW, I'm calling it mould for lack of a better term.
Response to the comments
I don't think it's tar (surely tar would be black?) Also, we've had this type of shed roof before (the old shed collapsed last year due to a burst water main), and this is just a replacement. Admittedly, the brick work is far superior in this shed.
The first picture is of the inside of the roof. All the roof is now like this. When new, it was black.
The second picture shows some of the brown drops of liquid on a box.