If you have found out that currently you can't learn the engram for the Obsidian Foundation and therefore neither the corresponding floor or floor corner piece then you can simply spawn in the blueprint for each and put them in the UC Smithy.

This way you don't have to cheat spawn in each item meaning you will still need the materials and you will earn xp from making them.

If you are on a server and are not the admin just get the admin to spawn them in and place them in your UC Smithy for you.

The cheat codes:

Foundation (blueprint):
cheat giveitem "Blueprint'/Game/Mods/UberCrafting/Structures/Foundations/Floor/Obsidian/PrimalItemStructure_Obsidian_Foundation_UC.PrimalItemStructure_Obsidian_Foundation_UC'" 1 1 1

Floor (blueprint):
cheat giveitem "Blueprint'/Game/Mods/UberCrafting/Structures/Ceilings/Normal/Obsidian/PrimalItemStructure_Obsidian_Ceiling_UC.PrimalItemStructure_Obsidian_Ceiling_UC'" 1 1 1

Floor Corner (blueprint):
cheat giveitem "Blueprint'/Game/Mods/UberCrafting/Structures/Ceilings/Corner/Obsidian/PrimalItemStructure_Obsidian_Ceiling_Corner_UC.PrimalItemStructure_Obsidian_Ceiling_Corner_UC'" 1 1 1