I am assuming kits just loads up from here (copy/paste data) and doesn't do much else.  so maybe have it hold a height modifier.  1.0 or 1.2 or 1.5, etc

or have it sample the terrain where the player's cursor is looking and maybe give them a notification to look up or down 

or have a ghost image of something that will show the relative bottom of the prefab floor(s) so the player can properly place the "base"