SOLUTION
with the help of @mrjj i found solution. It's just that instructions were not clear on tutorial
Steps
get the Qt creator source : git clone --recursive https://code.qt.io/qt-creator/qt-creator.git
set qmake version . your qmake version should be close to the qt version you are using . for e.g. if you are building for 5.10 your qmake should also use 5.10.
you can set qmake version by
sudo mv /usr/lib/x86_64-linux-gnu/qt-default/qtchooser/default.conf /usr/lib/x86_64-linux-gnu/qt-default/qtchooser/default.conf_orig
sudo vim /usr/share/qtchooser/my_Qt_5.10.0_Desktop_gcc_x64.conf
<Qt_dir>/5.10.0/gcc_64/bin
<Qt_dir>/5.10.0/gcc_64/lib
ln -s /usr/share/qtchooser/my_Qt_5.10.0_Destop_gcc_x64.conf /usr/lib/x86_64-linux-gnu/qt-default/qtchooser/default.conf
check qmake by qmake --version
mkdir qt-creator-build
cd qt-creator-build
qmake ../qt-creator/qtcreator.pro
4. ```
cd qt-creator-build
make qmake_all
make -j <number-of-cpu-cores+1>
wait for some time . it will take long time to build.
now you have both source and build of Qt creator . Now just follow the wizard and point the qt soruce and build locations
build and run
voila !! \0/
