Put a tile prefab in the world of your choice. Hold down the Ctrl key, and pull it in an axis' direction. You may have noticed a little snap that you wouldn't see when moving normally. This is due to unit snapping.

Grid snapping is a really useful tool when it comes to building stuff inside Unity. Instead of punching in numbers all the time when trying to set the positions of all of these tiles, we can just set our Snap size to be the size of our tiles 3.2 x 3.2 x 3.2.

Go to Edit | Snap Settings; we can change the value to snap easily by changing Move of X to 3.2 and Move of Z to 3.561, taking into account the wall's thickness.

Now that we have the snap settings working correctly, we will place a hallway to start our level and reset its Position property to (0, 0, 0).

Next, duplicate the mesh by hitting Ctrl + D, and...