Here is some useful building tips I learned while playing:
Buildings are built in steps.
When you click build the game generates these steps based upon the existing surroundings.
If you place two buildings next to each other and try to build them at the same time the building steps generated wont have accounted for the building not yet built next to it so building will cease when some scaffolding or ladders cannot be placed to continue.
Other than that if the game lets you place the building it can build it.
Building steps include the removal of ladders and scaffolding.
Don’t design buildings with pockets in walls where hearthlings and ladders or scaffolding can get trapped. You may build ladders to get a hearthling unstuck but trapped ladders and scaffolding most likely cannot be reached for removal.
Some build steps cannot be anticipated by the generator such as the need for a ladder to be placed to reach the roof where a ladder has been anticipated to place a planter in a higher window. Just place the ladder to reach the roof for them.
The generator sometimes makes errors in planning. On rare occasions I found ladders placed in walls sticking up through a window for example. I just placed a ladder against the wall to the under lip of the window and a hearthling was able to remove the ladder. More frequently furniture will be placed before a ladder is built to place a lantern or curtain and I will have to have them pick up the furniture so they can finish with the lantern or curtain.
On complex buildings it may be better to not include furniture in the design and place them after the structure is built.
You can place building without clicking build so you can layout how and where you want your structures to be. When you are ready just click and build one at a time.
If you saved a design where you have a foundation on an upper and lower terrain elevation the game currently will not allow you to place the building in the same manner. If you want to save such a design save it in as two buildings then place and build one then the other.
In short if they stopped building it is always because there is a step that they cannot complete because of some obstacle or lack of materials.
I am sure there were other tips I had but I cant remember them at the moment.
I hope this helps. 
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