Many galleries have lost their roofs, but excellent examples are preserved under the vast bogs of Sligo and Mayo. In Behy, a recently excavated tomb on the north coast of County Mayo, tall slab consoles rise above the sides of the burial chambers to support the flat tiles. This monument consists of a pile of stones in the shape of a coffin, about 28 m long, delimited by a dry stone cladding, which is preserved in places up to a height of 1.5 m. To the east, a pear-shaped courtyard, 7.5 m by 5 m, also made of dry stone, leads to a gallery divided into two main bedrooms. An unusual feature is the presence of small side chambers or transepts that open into the gallery beyond segmentation. The whole monument was covered with peat, which reached a depth of 2 m on the edges of the monument. Before the excavation, only the rear chamber with its transepts was visible through a hole in the roof. Once there, the stones were traditionally assembled and mortared with a mixture of water buffalo manure and ash, but are now more often cemented together. Typically, the walls are first assembled, and then the keystone is gradually raised to the height of the walls by a wooden scaffolding, which is inserted at the alternating ends wood by tree trunk. Once the ridge stone is at the right height next to the walls, it is set up above the tomb. Alternatively, some tombs are built by pulling the keystone upwards from a manufactured ramp and then mounting the side walls below before removing the structure from the ramp so that the keystone rests on the walls. Often, but not always, the finished structure is decorated by a professional stone sculptor with symbolic motifs.
Sculpting alone can sometimes take more than a month.  There is a wide variety of megalithic tombs. The self-supporting unicameral dolmens and portal dolmens found in Brittany, Denmark, Germany, Ireland, the Netherlands, Sweden, Wales and elsewhere consist of a large flat stone supported by three, four or more menhirs. They were covered with a pile of stones or mounds of earth. Unlike other types of Irish graves, passing graves are located on hills or ridges and are usually grouped in cemeteries. The actual number of Irish passing tombs is difficult to estimate, as many round mounds that could contain such tombs remain unopened. A number of about 300 seems likely, but this will of course be reinforced by future excavations. The tombs are largely limited to the northern half of the country, but scattered examples can be found in south Leinster and northern Munster. Four large cemeteries, Bend of the Boyne, near Slane, Co. Meath, Loughcrew about 65 km to the west, in the same county, Carrowkeel, Co.
Sligo, 90 km. to the northwest of the latter and Carrowmore on Sligo Bay stretch across the country from the Middle East to the northwest, accounting for nearly 50% of the total number of known graves. The metal was worked in Ireland before 2000 BC. J.-C., and a type of megalithic tomb that may have been used by these early metallurgists was the wedge-shaped tomb, which consists of a long stone-lined and covered gallery placed in a wedge-shaped stone mound that narrows wide towards the back of the tomb. The so-called cutting ceramics found in some of these tombs suggest links to copper mining, particularly in Kerry, but other places on the limestone pasture of the highlands, such as the Burren, suggest that shepherds may also have been involved in its construction. One of the finest examples is Labbacallee, Co. Cork, but they can also be found in many other parts of the country. Despite the fact that the portal tombs are relatively simple unicameral tombs, they contain several examples that are among the most spectacular Irish megalithic tombs.