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:dph http://www.ncbi.nlm.nih.gov/pubmed/15936325 GOC:cls http://purl.obolibrary.org/obo/go/references/0000021 GOC:dgh GOC:jid ]