cannot use custom message

edit

I have written a custom message file. I have done the necessary modifications in CMakeLists.txt. and I have run catkin build

So now when I do rosmsg list I can clearly see my custom message

roscustom_test/TheObject

also when I do this: rosmsg show TheObject I can clearly see

[roscustom_test/TheObject]
....components

However when I try to use it from a script.py I do

from roscustom_test.msg import TheObject

I get

from roscustom_test.msg import TheObject 
Import Error: No module named roscustom_test.msg

What am I doing wrong here?