This attic sheeting water damage looks pretty bad. The staining on the wood sheeting or one by twelve's, doesn't look good.

 Anytime you see a large stain, there's usually water damage to the ceiling and installation.

You should always check directly below any water staining that you notice on the lumber, rafters or roof sheeting for more damage to the home.

Water leaks like these can become a big problem if the water is leaking on any electrical, plumbing or heating materials.

The only problem I have with the picture above, is that I really can't tell 100% if this was a repair and the water damage was already repaired or if someone installed a attic vent improperly and that caused the water damage and staining.

There's only one way to find out, someone's going to need to go on top of the roof and inspect the attic vent.

There's plenty of room in the attic, and that tells me one thing, the roof is very steep and whoever inspects the attic vent and roofing for damage, should be a professional or someone who is very comfortable walking on steep roofs.

I don't recommend this to anyone lack the experience and common sense.