How to clean a copper roof
Soap, water, stiff bristle brush. Do not use wire brush. Spray nozzle on garden hose or extreme low pressure on power washer. Spray from topside down.
There are commercial and homemade products, but many wiill change patina of copper, often not to the best. But if you have chemical stain from droppings, it may not matter. Weak acids such as white vinegar or slightly stronger 10% horticultural vinegar, wear rubber gloves, protective clothing and eye protection. Extreme case may need soda, or soft pellet blasting, not sand blasting.
Measure twice, cut once.
Look at the nail, not the hammer. Watch the fence, not the blade.
If you hook your thumb over your belt you won't hit it with the hammer or leave it layin on the saw table.