private Component buildTypesPanel() {
		JPanel panel = new JPanel(new BorderLayout());
		panel.setBorder(BorderFactory.createTitledBorder("Block Types"));

		MemoryBlockType[] items = new MemoryBlockType[] { MemoryBlockType.DEFAULT,
			MemoryBlockType.BIT_MAPPED, MemoryBlockType.BYTE_MAPPED };

		comboBox = new GhidraComboBox<>(items);
		comboBox.getAccessibleContext().setAccessibleName("Block Type");
		comboBox.addItemListener(e -> blockTypeSelected());
		panel.add(comboBox);
		return panel;
	}
Define the Main panel for the dialog here.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/memory/AddBlockDialog.java