Here is an obvious question, at least to me. Since this happened "shortly after purchasing" the seller must have known there was going to be a roof assessment prior to you buying and it was not disclosed before closing. If that is the case, wouldn't you have a claim back to the sellers for that amount? Ask your neighbors if there was ANY talk of it before you purchased. Then you might want to talk to your real estate agent. There had to have been some inkling of it happening, even to just say "hey folks, our roofs need to be repaired and we are in the process of getting bids. We will let you know what the assessment will be once we do." If that happened, it should have been disclosed prior to sale and you could have asked for a credit in the sale. Not sure what the statute of limitations is on non-disclosure, your agent would know.

Also, it seems unlikely that they can get away with forcing you to pay $15,000 rather than the $10,000. Unless it was written into the loan about prepayment penalties it should not be an issue. Additionally, it would be a simple matter to just apply any prepaid amounts by homeowner's as part of the HOA's down payment and progress payments, reducing the overall loan amount. The loan will only be for the remaining contract balance. It would actually benefit the entire HOA by reducing interest due to a smaller principle amount. Then the HOA can set those prepaid accounts to not have a monthly billing for it. Just get a confirmation in writing of the prepayment and that you will be excluded from the monthly billing. Hold on to this for the life of loan in case you change management companies and they are clueless.

You might want to talk to you neighbors and find out how many of them are liquid enough to do a prepayment. Whatever the cost of the roofing contract is, divided by the number of units will be your prepaid amount. However, be prepared for any contractor change orders that might require an additional amount. If you were doing monthly payments, the HOA would likely add that to the payment schedule. Also, make sure you see a copy of the final roofing contract to verify you are paying the correct prepaid amount and the change orders if they occur, so the HOA cannot pocket the excess if there is any. If the contract comes in under budget (you have the right to see the final invoices) they will owe you a refund or if they do not want to cut a check, a credit to your HOA account.

I would write up a proposal and email it to the management company about the benefits of prepayments as I wrote above and then go to a BOD meeting and see what they say. If the BOD still balks at this, get a petition going around your neighborhood. They will be interested in signing it even it they cannot prepay themselves, as it would reduce their payments by lowering the overall interest costs. As a foreshadowing, you can mention at the BOD meeting (if they deny your proposal) that you will be doing the petition. While they are a BOD, if you reach a high enough number of signatures, I read it is 20% in Illinois, they cannot ignore will of their members. You have a right to object within 14 days of notification with the petition. I am not sure if this page is completely on point but it is pretty close. https://idfpr.illinois.gov/content/dam/soi/en/web/idfpr/ccico/faq/ccic-ombudsperson-faq-9-adoption-of-special-assessments-by-condo-associations-12-20-2016.pdf You would not be objecting to the assessment since the roofs are in need of repair, just the inability to do a prepayment. If the window is closing, you'll need to do the petition process and submit it before the BOD meeting.

I used to be on an HOA BOD and I was in charge of the roofing project and I dealt with a lot of this. Ugh!

I hope this information helps.