Much like AutoCAD and Photoshop, Layers in FormIt allow you to manage the visibility of objects in your scene. We are going to create a layer to save and hide the building mass for analysis in the future.
Go to the Layers Palette and click the + sign three times to create three layers
Double click the layer names to rename them Massing, Floor 1, and Plan Image
Select the main building group and choose the Massing layer from the Selection On: drop down at the top of the Layers tab
Single click to select the plan image group and put it on the Plan Image layer
Select the main building group again
Press Ctrl + C to copy, and then Ctrl + Shift + V to paste the mass in the same place
The new copy is still selected. Right click and choose Make Unique (MU)
Note: The new Group is now severed from the original and they will not update each other any longer
Single click to select either of the main building groups
Put the group on the Floor 1 layer using the Selection On drop down in the Layers panel
Uncheck the Massing layer to hide it - and keep it safe from any accidental edits!
Double click the Floor 1 Group to edit it. Re-name the group Floor in the Properties palette
Single click the top face to select it. Click again to start dragging the face down, and start typing 1', and a dimension box will appear. Hit OK when you've entered the value. The resulting floor should be 1' thick
Double click off in space to exit the group