Xanathar's downtime days suggest that a character can build an object worth about 10gp in a day's work. So I guess it depends on how much a portcullis is worth, how we're doing for materials (I guess it depends on what we have access to) and if we have the tool proficiencies, and the required tools.
Based on what I know of the resourcefulness of people, I bet we could have a decently made door pretty quick, but I'm not sure we have the resources for anything made from metal. we could easily make a portcullis of wood, I'm sure, and probably back it up with a door.
Who's got Carpenter's, Leatherworker's, Smiths, or Mason's Tools proficiencies?