The phrase "ample headroom" means that there is enough space or capacity available to accommodate something without any limitations or restrictions. Full definition
But if you're looking at a wide open space with ample headroom in the centre, it might be worth building stairs up through a closet, and adding insulation and heating ducts. (moneysense.ca)
The stepped up roof provides ample headroom for the middle and third - row passengers. (carwale.com)
Its upright cabin looks odd, but provides ample headroom not only for those in front, but even for large adults forced to ride in the back seat. (automobilemag.com)