Metal roof with fiberglass and plastic underneath

We recently bought a property with a shop/art studio building with a metal roof. The metal roof was installed directly over battens with no tar paper or other material between the batten and the metal. The prior owners would heat the building with a wood stove and perhaps sometimes electric heat when doing art projects. At some point about 8 inches of fiberglass insulation was installed beneath the battens. Underneath that a lawyer of clear plastic was added. This seems like a horrible combination. It also makes it very difficult to locate any leaks. We are on Vancouver Island, British Columbia, Canada, which is a mild Pacific Northwest environment with a fair amount of rain. Note that the future use of this building will be as a shop/barn. It will be a completely cold building. I am thinking of removing the fiberglass and plastic and just seeing whether there is any condensation. All opinions and suggestions welcome.

Does the leak show only when you heat the space?

What we need to do is isolate it as either a result of interior or exterior humidity. The repair for either is different.

Good question, but the answer is no. We have not ever heated it and we plan to use it strictly as a cold building. I have had three leaks, one by a wood stove chimney and two other small leaks I am currently tracking down. The chimney leak has been stopped for now and the chimney will be removed when drier weather comes. Hay storage and wood chimneys do not mix well. I am pretty sure that the other two small leaks will be tracked down when I remove more of the fiberglass and plastic. The roof is about 32 years old and it is not surprising that some leaks have shown up as there probably has been very little maintenance. My question is not so much about fixing the leaks as about whether all of the fiberglass and plastic placed under the battons should be removed and, if so, whether to put something else in their place.

Any pics of the roof? Could be an exterior condensation issue or a leak via bypass in the roof assembly.

Sorry, but this line of discussion is really not addressing my question. The leaks are a minor concern and can be addressed if the fiberglass and plastic underneath are removed. My question is whether the existing roofing system makes sense. Again, it is metal roofing directly over the battons, with fiberglass underneath the battons and then a clear layer of plastic underneath the fiberglass. This seems like a bizarre system to me, unlike anything I have ever seen. What I want to know is if it made any sense to build it that way and then go from there.

The answer is...we don't know.

If you are not currently heating the space, the likelihood is that the drips are not a result of interior humidity that is condensing on a cold surface. That that point, the source of the leak points less to the fiberglass and plastic and more the roof surface whether that be condensation on the backside of the panel or just a bulk moisture transfer via a leak.

The system you describe (i.e. insulation and vapor barrier) is an accepted application and does work when it is deployed properly.

The reality is that solid decking is more more foolproof and will make it more resilient against what is a normal difficulty of purlin/batten installed systems in condensation.

I think that tells me what I need to know at this point. Thank you.

Good luck and feel free to post as you get further into the project.