Hey Appnut
I have a dryer that vents through the roof. If I had it to do over again, I too would NOT move into a house where the dryer vents through the roof. I've dealt with this since 2004. The first few years, about every 3 months.....YES, THREE months, drying times would start going up. I had to get the leaf blower out....but that wasn't all............ Then, I had to go outside on a ladder to the edge of the roof, tie a brush to the end of a long poll and get some of the lint off the roof cap....the roof pitch is way too steep to get on the roof. I did it once and never again. The roof cap is at the very top of the roof.
A few years later, I read this post about a lady and her husband living in a condo did had the same issues. She said her husband had this idea to put a paint strainer in the piece that connected the back of the dryer through a wall. About every 3 weeks they would go back there and clean it out. At first I was discussing this with her thinking this is a fire hazard. She said they had on issues for years and it had kept their entire vent run CLEAN! She said it was a pain to get back there every three weeks but not nearly the pain as it was cleaning the entire vent run a few times per year.
So......about 2009 or 2010, I bought a paint strainer. It's easy for me to get behind my dryer so I put it into the piece that connects the back of dryer to the wall. Every 2 to 3 weeks, I get back there and take the paint strainer out and clean it with the vacuum and put it back. Dry times are fast, the dryer does not get hot, and it keeps the vent run clean. There's not even any lint in the piece that connects the dryer to the wall. It's totally clean. It takes me about 5 to 10 min's every 2 to 3 weeks to clean it. This is what I've been doing all these years and no build up. Now, I'm diligent about cleaning it and not letting it go too long or clean it more frequently if I dry something that causes LOTS of lint.. I'm the only one who does laundry here so it's no big deal. My dryer is electric and it's approaching 14 years old with no repairs. Knock on wood. It definitely would cause a block if not cleaned at least once per month.
The thing is - you shouldn't have to do this at all! Venting a clothes dryer through the roof is amazingly stupid!