Annoying bug when trying to build slab to reach second floor.
To build stairs directly to a house is also not possible due to the building bugs when hearthlings don’t do anything.
Can’t Put Slab Here Above the Other Slab
Getting a Red X
This really needs a fix it’s like when slab reaches second floor you can’t place it.
Feels like the only way to build creative now is Instant Building.
Update
I tested other things like remove a 2x2 part of the second floor and adding a ladder for temporary work around since we cant make stairs to second floor after removing the floor on second floor.
Problem is that this don’t work either it’s also broken you cant place ladders to the second floor
Hope the Devs read this because this is a pretty important building problem that needs to get solved.
Update 2
This works perfectly in an old alpha that i have saved on my pc
StoneHearth Alpha 0.10.0 (alpha_10_5_3)x64 build
I found that if you build a 2-floor structure and place slabs on top of a floor, the building wont complete. I tested in multiple buildings and was not able to be built. Only when i left a hole in the 2nd-floor and added the slabs after completion was it able to be built.
Yes there is also this bug that your describe.
The thing seems to be that if you remove second floors floor when building is done there is still an invisible floor left that blocks adding ladders and slabs there.
The way you describe with leaving a hole is a temporary solutions until they fix this.
Thanks for sharing that 
So most likely there is some bug when you remove floor’s that they are still there but invisible
Update 2015-11-01
So i have confirmed this bug not how it exactly works but if you build a two story house and you decide to remove parts of the second floors floor the parts you remove with the “rubber tool” are still there but not visually and hearthlings can walk on top of it and you can’t put things at this place for this reason.
For anyone interested in it i can post my upcoming youtube video where i show it early on in the episode