The formation of a single row of glia at the dorsal midline of the developing neural tube. This region provides inductive signals for the specification of neuronal cell types and of the specification of neural crest cells. The cells comprising the roof plate are the precursors to radial glial cells. [ GOC:cls GOC:dgh GOC:dph GOC:jid http://purl.obolibrary.org/obo/go/references/0000021 http://www.ncbi.nlm.nih.gov/pubmed/15936325 ]