Solar in Illinois has to respect open prairie wind, hail, and a roof that may already be tired. A clear farmstead sky is not a maple-shaded town lot. Snow will sit on a low pitch. Modules add weight and they add uplift when a storm gets under the array. The roof deck and the rafters come first. If the shingles are already bruised, say that before you talk about the sun.
Silos, a south windbreak, and a neighbor's tall wall all cast shade. Say what stands south of the ridge, and whether leaves cover the slope in summer. Winter sun rides lower and may clear those crowns or may not. A hip roof, a gable, and a low-slope porch are different mounting conversations. The surface has to be something you can fasten to without turning the next rain into a leak.
Hail that bruises shingles can also mark module glass. Wind that peels a ridge can work on clamps and rails. Ask how the array is tied to the structure, not just how it sits on the shingles. Critters nest under arrays that create a warm gap; if you already hear them, say so. Snow sliding off metal in a sheet can be steered by an array toward a door.
Illinois production swings from long summer days to winter weeks under a snow blanket, and the equipment has to live with both. An inverter needs air; a closed attic is a poor closet. Say if the main panel is old or already full. If the roof is due for replacement, do that in an order that does not install twice. Say whether the building is a house, a barn, or both.
Lead with the roof you have, the shade you can see, and whether hail or wind has already marked the slopes. Name the town and which way the ridge runs. Illinois sky is useful only if the building under it is sound. Call the number on this page.