Mono crystaline panels typically have higher efficiency and better low light performance than Poly crystaline thereby typically providing more energy production than an equivalently rated poly crystaline module.
Keep in mind the size of panel as compared to your available roof space. Typically mono crystaline panels will be smaller than similar output poly crystaline panels due to their higher efficiency.
PV panels power output drops as temperatures exceed 25 deg C in accordance with their temperature coefficient.
The glass cover on the panels have been designed to withstand rain, snow and hail and are very durable with warranties of 10 years or more in most cases.