Warning— Do not eat or drink while watching, or stuff will spray from your nose and mouth!
I was under contract with NASA for two projects (Surveyor and Apollo) as are 99% of the spacecraft people. Most engineers usually do NOT come up with simple solutions. We are the Rube Goldbergs of industry.
I've tried a good number of squirrel resistant bird-feeders but all failed until the one I bought two years ago. That one works...even though with each year, the young ones give it a try. But, so far, they always are thwarted.
Your Squirrels must be extremely stupid, unless the tin roof is greased. When my late wife fed the birds I tried something on the same order as yours and the little bastards came in off the deck roof and hung upside dow to traverse the rafters to get to the feeder the had a sloped metal lid on it. The best deterrent was Buttons our Yorkie he hated the squirrels!!
I put my feeder on a pole that is away from anything that a squirrel can leap from or hang from. Unless they grow wings, they are doomed to failure. You should do the same. As I said, this bucket on the pole has worked 100% of the time for three years. My squirrels are as smart as yours. Maybe it's your intelligence that's in question.
Although it cost the great sum of one dollar for the plastic bucket from the store of the same name, it has defeated every critter in the three years that they have attempted to get to the bird seed. The feeder is about six feet off the ground. Only tool needed is a hole saw for the center of the bucket bottom. I have not patented it, so its my gift to all.
I could not believe that I would see this little guy in the middle of a drought here in Texas. I have never seen one that wasn't green. He was in amongst the Pentas in our rock garden.
I made these shots with my excellent Sony A65 and Sony 18-135mm zoom lens at F5.6 and distance of about 3.5 feet. Its a great combination that stays on my camera most of the time.