Although you cannot create a Floorplan in Event Temple, you can still add them to Documents using an Image Element.
Locate the Document you would like to add a floorplan too
Drag the Image Element to the location on the Document you would like to display it
Double-click the Image Element to edit the element
Ensure the Image Source is Uploaded File
Choose File and pick the floorplan image
Apply
Don't forget to save the Document
If you would like to add pre-selected Floorplans to Events you can use this method.