I am a realtor in CA so maybe the rules are different where you are but if you are in your due diligence period you should have the ability to continue getting quotes on items that may need repair. If I think the roof is nearing its end of life I would probably want to know what that expected cost is going to be to fix it whether I'm getting that from the seller or I'm going to begin planning to cover it myself down the road. That being said, you may need to pay to have the vendors come out, sometimes they are free other times they will charge you to give an estimate, provide an inspection report, etc. And just because you get a bid it doesn't mean the seller will have any obligation to cover any of the findings or pay for the person that came out, but it does at least give you more information.
In a hot seller's market you probably aren't going to get much for items that are old but still functional, ie, if the water heater works, the roof isn't actively leaking, then yes a lot of seller's won't chip in for that. Same for minor aesthetic fixes, especially if you were aware of them going in or could have easily seen it prior to writing an offer. BUT, I don't see why you cannot ask for a credit for legitimate issues (safety issues, broken items that were not obvious or visible when you initially walked the property, items not functioning the way that it should). You have a 100% chance of not getting any concessions if you do not put in a repair request but at least some chance if you do. Especially if your real estate agent can make the case that every buyer will care about these issues. Talk with your real estate agent to see if there is any harm that they can see in putting in a request. Most cases, the worst that will happen is the sellers says no and you're not in any worse of a position as you are right now, but they may say yes to at least a few things.
And if they say no, then like other posters have mentioned, you can always walk away. There will always be another home to write on (though if it is a really hot market there then the equivalent home may quickly become more expensive than the one you have in contract right now).
One final question, since this is a townhome, have you checked with the HOA to see if the roof is going to be your responsibility? Some HOAs cover the roof.
Best of luck with it.