moose-gui is installed to <prefix>/share/moose/gui folder.

CMakeLists.txt

 CMAKE_MINIMUM_REQUIRED(VERSION 2.8)
 PROJECT(moose)
 
+## Default install prefix. When building packages, such as on launchpad, we need
+## to modify installation prefix.
+if(DEVELOPER)
+    option(CMAKE_INSTALL_PREFIX "Install prefix" ${CMAKE_BINARY_DIR}/_install)
+else()
+    option(CMAKE_INSTALL_PREFIX "Install prefix" /usr)
+endif()
+
 include(ExternalProject)
+message("[INFO] Installtion directory is ${CMAKE_INSTALL_PREFIX}")
 ExternalProject_Add( moose-core
     PREFIX ${CMAKE_CURRENT_BINARY_DIR}/_moose-core
     SOURCE_DIR ${CMAKE_SOURCE_DIR}/moose-core
-    CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=${CMAKE_BINARY_DIR}/_install
+    CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
     TEST_BEFORE_INSTALL 1
     BUILD_IN_SOURCE 0
 ) 
+
+## moose-gui
+
+set(MOOSE_GUI_DIR ${CMAKE_SOURCE_DIR}/moose-gui)
+add_custom_target(moose-gui ALL)
+add_custom_command(TARGET moose-gui
+    POST_BUILD
+    COMMAND ${CMAKE_COMMAND} -E copy_directory ${MOOSE_GUI_DIR} 
+    ${CMAKE_INSTALL_PREFIX}/share/moose/gui
+    )