Cannot lay builds in Map

Hi All,

I have created a map using the Kevin Floating Island template.

After building for quite some time, I ran my map and when I went to build floor/wall/stairs etc. it didn’t work:

I’m not sure if the reason is because I built in the sky and not on the ground, or if it is because I used the obstacle course gallery props?

These are the current settings for all obstacle course floors:

Any help would be much appreciated!