To dream of such an edifice is to recognise the importance of death and the rites of passage associated with it.
2- When we come to an important change in our lives we may wish to mark the passage or transition in some way. We have a need to have other people recognise or appreciate our efforts.
A sarcophagus would indicate that there is a good deal of ego still to be dealt with within as.
3- Spiritually, death indicates both a change of state and a change of status and a sarcophagus is a symbol of such change.