How can I get my settlers off the roof without a mod?

Here's the easy way. Looking at them (the way you are now), open the console. With the console open, click on one of them to select them and type into the console moveto player. Press Enter and it will teleport the selected NPC to you (you'll have to close the console for it to take effect). Do the same for each NPC up there.

There are many ways to get these people off the roof.

1. create stairs and wait for them to get off or go to sleep.
2. create stairs and add food, or create a scavenging station, or create a shop nearby. Assign each settler to any of those.
3. create stairs and create a bell to call settlers nearby. Ring the bell to call the settlers.
4. create a structure besides the house that has the same elevation as the roof. Place a roof over it and add a tv and sofa in front of the tv. Connect the structure to the roof or create stairs to get onto it. Wait for them to go and watch tv.
5. create a drink stand far away from the house. Assign a settler to it. They will go there on their own before the end of the day.