What’s this?

Discovered this on our roof this morning… on top of the surface is now a reflective ‘material’, fully transparent, odourless and tasteless, with very low viscosity and high reflectivity, almost mirror like.
Wasn’t there yesterday, can’t remember having seen it there the last few months…

Any ideas?

Will have to get to backblipping soon, just too busy in the first school week of the kids.