What is the ruling on building a grave or a tomb?

There is no religious objection to constructing a grave in order to prevent it from being lost, as long as it is done without ostentation or extravagance, and to placing a simple stone or similar plaque at the head of the grave bearing information identifying the deceased. When the Companion Osman b. Maz‘ūn (r.a.) passed away, his funeral was buried outside Medina at that time. The Messenger of Allah (s.a.s.) requested a stone to mark Osman’s grave, and when the stone was brought and placed at the head of the grave, he said, “With this, I am marking my brother’s grave, and I will bury those from my family who die beside it.” (Abū Dāwūd, Janā’iz, 63 [3206])

However, it is not considered appropriate for graves to be built more than one or two spans high, for buildings or domes to be constructed over them, or for excessive words of praise or expressions of complaint about death and fate to be inscribed on the gravestones beyond basic identification information.

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu