i looking to build a light bar i have a couple of questions frist how thick of tubing would be best also hows the best way to mount it i wanted to use my roof racks but been told it wont hold if i hit some thing and finaly hows the best to mount my kcs

 

Check out this light bar I made on top of the bumper I made.
I literally took a reciprocating saw to an old tread mill.
I believe it's 2" by 4" rectangle steel. Plenty sturdy.
I agree with others don't mount to the stock system. I would buy/build brackets that attach to your rain gutters which hold up the light bar.

Just google "jeep cherokee rain gutter roof rack" maybe this will give you ideas

 

Made one out of a bathroom safety handle. Cost about 50 bucks for th hardware and silicone. Looks decent. Its stainless steel so it ain't gonna rust.

 

That sounds dang clever!
Got a pic of it?

 

Can get u one today sometime if I remember. If not pm me and remind me.