Using OS Roam:
At the most zoomed out level in OS Roam a very basic map is displayed showing country outlines and capital cities. There is another variant of this map available through the Basemaps menu which only has relief displayed. Both these maps are only available in colour but do show the whole country.
If you only need an outline of a smaller section, then this can be created by zooming in to the Metropolitan View, which displays the OS product called Strategi. This map can be customised through the Map Content panel to turn off all features apart from the Coastline.
Using OS Data Download:
To create an outline map in a GIS/CAD package outside of Digimap Roam we recommend downloading the GB National Outlines dataset, which can be found in the Boundary and Location Data section in OS Download. This is available in SHAPE, MID/MIF, and DXF formats for use in common GIS and CAD packages.