Tried to copy and paste a link to an answer on this same exact question, but doesn't work for some reason. Do a search for "roof lights" on this forum. Go to page 5 and find the thread on "light size." There's a great example from someone who did a great at home fabrication job that includes an easy to follow schematic.
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2004 X, 5 speed manual, ARB bull bar, Shrock sliders and skid plates, Hella rooflights, Nitto Terra Grapplers 265 75 16's.