What can I do if my building won’t pay for the damages?

Your claim may be through your renter's or auto comprehensive coverage. I cannot comment on the buildings liability without additional facts.

What leaked? There is no way water should have ruined the paint on your car. It's hard to answer your question without more information.

Generally, if there was nothing the owner/landlord did which was negligent, they have no responsibility to pay for damage to your personal belongings. You may be able to make a claim on your own renters insurance if you had that. If you didn't, if you had comprehensive insurance on your auto, you may be able to make a claim against that.

Pay to have the car repainted and sue him in small claims court. Be sure to take good pictures before and after you paint it.

I assume this is either a building you work in or live in. In either case, the building is liable if they knew about the leak and did nothing to prevent damage to you or others. The key will be proving their knowledge. Also, keep in mind that we are a contributory negligence state. That means, even if the building did know and you can prove it, if they can show that you were negligent as to where you parked, i.e. they put up signs you ignored or your saw the leak, then you may not be able to collect.

This is a potentially tricky issue, as it's unclear without reviewing your lease, as well as relevant case law, whether or not what they say is true. You certainly have claims that may well be viable to pursue in court if they're unwilling to cover the damage, but anytime you go into court it can become a risky proposition with no certainty of the outcome. It's unlikely, though not impossible, that such claims may be covered in Oregon's Residential Landlord Tenant Act, but you may well have a civil tort claim that might be worth pursuing. With small damages such as these, some attorney will consider taking the case on a contingency fee basis or a hybrid basis, as attorneys fees are potentially available to the winning party.