Metal Shears - Electric.
These are great and can save you valuable time.
The cost on these will run approximately $200 dollars.
Nibbler - This can be an attachment that will attach to your electric drill.
This is a great tool for cutting curves and it will cut straight lines just as easy.
These attachments usually cost about $40 to $50 dollars, but very well worth it.
Cutting blades - These are usually either an abrasive wheel or a small circular saw blade, one for cutting metal, designated for ferrous.
Your circular saw blade may be either the small 3 to 4 inch, or a 5 to 7 inch blade that will fit your regular circular saw.
All of the blades designed to cut steel are usually very thin and most have carbide tips.
These blades run anywhere from a few dollars up over the hundred dollar mark.
The abrasive wheel has two rather large draw backs.

• They Can Break - Because they are very thin they will break easily if they get in a bind or if you force them too much.
  When they break pieces fly everywhere.
  
• Because of the edge they leave most manufacturers recommend not using them.
  This edge leaves a place where rust and corrosion can start.
  

Metal Hand Snips - There is no way you can get by without metal snips.
There are three different styles.

• Straight
• Right Hand
• Left Hand

These different styles are for cutting straight or making a right or left hand turn while making your cut.
Metal Snips can be purchased at your local tool or hardware store for $25 to $30 dollars a pair.
You will be ahead of the game if you purchase all three sets.
Safety Glasses - You must always wear some type of eye protection.
When working with metal there is always a chance of small metal chips flying through the air.
You don't want any of them to hit your eyes.
Good luck with your project.
Make sure you understand all that is needed when putting on a metal roof.