Roshan control is often the deciding factor between a win and a long, drawn-out loss. Looking at
https://www.itechgyan.com/dota-2/ will help you understand the spawn timers and the different rewards Roshan drops on his second and third deaths. Generally, you want to look for a pick-off on the enemy mid or carry before heading to the pit. Having a Medallion of Courage or Solar Crest makes the process twice as fast by reducing Roshan's high armor. Don't forget to use a Scan on the high ground near the pit to make sure the enemy isn't waiting to jump in and steal the Aegis. If you can secure the second Roshan, the Aghanim's Shard and Cheese will give your team a massive advantage for the high-ground push.