Roofs are designed to be installed on a slope. They are designed to be rained on and then dry out. Debris on your roof that traps water, causing the water to go sideways, can and does cause leaks in roofs. The simple solution is to keep your roof clean. Roof cleaning is not complex or difficult but safety is a very important consideration.
This information is published for your benefit. Use at your own risk. By reading this material, you consent that I am not liable for the information here. I am not telling you to go up on your roof. This material is for educational purposes only.
Going up on a ladder and/or roof can result in a life-threating fall. It is a serious matter. Not only is there some non-typical exercise involve, but roofs are not flat. They require articulatioin of your ankle, involve a risk of slipping, no safety rails etc. Many are not used to walking on slopes, and would be best to hire an insured professional who has signed a letter of indemnification for you (holding you harmless if they are hurt while they are on your property for that day).
Extension ladders can slip and fall. If you are going onto your roof, and you have an extension ladder, then I strongly encourage you to look at ladder arms. Ladder arms fasten around the top rung of your ladder and are designed to rest on the roof instead of the slick, flexible, easily-scratched gutter edge. And! ladders arms are very inexpensive (especially compared to a hospital bill). They run about $25 and will last for many years. Most home-builders stores carry ladder arms for about $25. What a deal! I used ladder arms every year I was in business and would not have even considered going up an extension ladder without them. Ladders against gutter edges are slippery, dangerious and very risky in my opinion.
Ladders have weight ratings which MUST be followed. If you weigh 300 lbs, don't go on a residential ladder rated for 200 lbs.
Ladders have feet. They need established firmly. If placed on a slick floor, they can slide out. Even if a person is holding a ladder, it can knock their feet out from under them. Bases of ladders on slopes may need supported by a 2x6 braced with rods driven into the ground etc
Never risk your life to save a few bucks. That's foolishness.
To find ladder arms, a ladder accessory, you can do an INTERNET search on "Werner Universal Stabilizer" (about $25) or "Werner AC96 Aluminum Ladder Stabilizer" etc.
I recommend inspecting your roof every year or two for weathering and wear.
Branches are typically easy to spot on your roof. After big storms, and with trees nearby, has a branch fallen on your roof. The concern is for punctures in your roofing material, roofing felt, or roof sheating. You may need to put up a ladder on the side of the roof and look to see if a hole has been caused. Depending on your experience, you can use a broom or something to pull the branch off the roof. You might be able to use a zoom on a digital camera to get a close up look at any possible damage. Anyway you look at it, the branch should be removed.
Leaves and needles will often blow off a roof and go many will end up in the gutter. However, if you have valleys in your roof, these become resting points, especially in longer valleys in roofs. Leaves and needles in valleys of your roof may allow water to go through when they are dry, but when they become wet, they lay flatter and block water from flowing off the roof. Also, when they trap water for longer periods of time, they soak into the shingles (yes, shingles do hold water) and the moisture will saturate roofing felt and can soak into the plywood roof sheathing.