I would like to Draw UML Diagram on LibreOffice Draw but I would like to have the shapes done.
Download the UML shapes from http://www.lautman.net/mark/coo/index.html. Then go to View → Gallery and create a new theme called “UML”.
Finally, click each shape and drag and drop it into the gallery. This is somewhat tricky because you must hold the mouse down for about a second before dragging, as explained at Adding Graphics to the Gallery - LibreOffice Help.
These instructions were adapted from Drawing UML diagrams in OpenOffice Draw | Mark van 't Zet.