I have a 2005 Chevrolet Colorado and I’m planning on putting some exterior lighting on it. Specifically two LED Light bars. I am having trouble figuring out what size light bar to put on the upper windshield (it will be mounted at the very top of the windshield) in the picture I added some blue bars to show where I’m putting the bars. I would like the upper Bar to span the entirety of the roof, but not stick out past the sides of the truck. If anyone has done this to their truck, I would love to hear your advice and if you have any pictures, I would like to see those too if at all possible. Thank you!
Are your pockets deep . . . ?
There are several manufacturers of lightbars. I’ll throw out some names now
Federal signal
code 3
grote
whelen
By the way, lightbars aren’t mounted at the very top of the windshield. It’s better to put them further back. You’ll need to buy a complete kit, with wiring, control unit, etc.
There are lighbars for police, fire, towing, construction site, etc.
Exactly what is the intended purpose?
@db4690 It’s going to be an off road light bar for night driving in the desert and also a flood light for work
I am having trouble figuring out what size light bar to put on the upper windshield
Sorry I am not going to guess the length you need.
You need one of these to figure out the length you need. And they are cheap too.
Just measure it. What is the problem?
Um, you just draw the amount of the tape measure necessary to span the desired length and read the number. We can’t do that for you from here. 
If you’re afraid to scratch the paint, use a seamstress measuring tape.
If you’d like, once you measure it we can convert it to metric units for you. Or “king’s feet”. Or cubits.
I’ve measured the roof, my issue is none of the bars I’ve found give a definitive size with the brackets so I’m asking if anyone already has a bar on their similar truck, what size did they go with. I have a light bar on my 87 Ford Ranger that I measured for, but it sticks out about an inch on either side of the truck and I’m trying to avoid that. It sounds simple, but everyone that I’ve asked so far has had it done professionally, and I want to do it myself.
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Do what the pros do. Get one that’s longer than you want with lights adjustable as to their spacing, use a jigsaw to cut the ends to length, and move forward with centering and mounting everything.