Recently I just finished working with Denise Regan on doing a reconstruction of what the Ballymacdermot Court tomb may have looked like. Ballymacdermot is in couty Armagh on Slieve Gullion. Its a Neolithic tomb type called a court tomb because of its distinctive court at the entrance These are one of the earliest forms of tombs in Ireland and mostly found in the Northern half of the island.
The kern stones (the stones at the ends of the cairn) were no longer evident as it is believed that perhaps they were taken by locals to build their houses. So the kern stones around the edge of the cairn material as well as the cairn material is mostly gone so reconstructed here. Also the roof itself was missing but was believed to have been corbelled like shown.
During excavation they found the site had a definite end, as it had been sealed in the ancient past, so essentially had been closed as part perhaps of some ritual or to stop access to it from people who were still using it, when they werent supposed to. If it had just fallen out of use or people no longer believed in the same spirits or gods, they would have just left it fall apart by itself