private DataType chooseType() {

		int noSizeRestriction = -1;
		DataTypeSelectionDialog selectionDialog =
			new DataTypeSelectionDialog(tool, null, noSizeRestriction, AllowedDataTypes.ALL);

		tool.showDialog(selectionDialog);
		return selectionDialog.getUserChosenDataType();
	}
Create the actions for the menu on the tool.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/datamgr/DataTypeManagerPlugin.java