My garage runs into my basement. I only have one single car garage door. My basement wall is a block wall. My floor joist run parallel to the wall with my garage door. What I want to do is install a second single car garage door next to my existing garage door where a service door is located. In order to do this I need to knock part of my basement wall down and install a Header. I can copy the construction from my existing Garage door. Is there anything I should be concerned about?

Show us some pics. Inside and out.

You mean like the house falling on you while you are removing that wall? Yes, you should be concerned since you haven't even told us what the house is made from or how tall it is. In most places you will need to pull a permit and this may require blueprints and a structural engineers stamp. Have you tlked to the local building inspector yet to see what's required?

I would suggest finding someone to come out and look at the job that has done this type of work. Like a contractor. They even could give you a few tips if you offer to pay them for suggestions.