Using the Map Editor
Using the Map Editor is an official tutorial in two parts which goes through creating a new metaroom with the C3/DS Map Editor. Note: With the move from gamewaredevelopment.co.uk to gamewaredevelopment.com, the image files can't be seen in the tutorials.
Part 1 covers creating the background, making sure the room types and CA types are the same as in the official worlds, positioning the metaroom in the world map, how to create rooms within the metaroom, make doors connecting those rooms, give those rooms a room type, injecting it into your world, and making changes and removing metarooms.
Part 2 covers how to add in a favourite place, how to create doors that will take creatures in and out of the metaroom, a reminder that the room should contain some agents to make life more comfortable for your creatures, and how to make a lift.