Duplicate a selected object.
Select an object and choose Duplicate from the Edit menu. A copy will be made offset a small distance from the original.
Keyboard Shortcut: Ctrl+D
Hold in the Q key and drag an object to peel off a copy. When peeling off windows, doors and holes you must drag them completely away from the original before you'll see them.
Create rows and columns of objects by Q-dragging them the distance and angle you want from the original. Then just press Ctrl+D to repeat duplicating.
A Row of Windows:
Evenly Spaced Chairs
1. Drag in a chair
2. Q drag a copy to the right of the original
3. Press Ctrl-D several times to create a row
4. Choose Multiple Select from the Edit menu to select all the chairs
5. Choose "Group" from the Edit menu
6. Q drag the grouped chairs behind the originals
7. Press Ctrl-D to create more rows
If windows, doors or holes don't have space to put the duplicate - you'll get an error message indicating that duplicate could not be completed. Choose Undo if necessary.