Designing 

It's not rocket science

I describe how to design in my books & it is easy to do once you get
the hang of it.

Sit back & think about what you want the room to do for you. If it
is a bedroom addition then it certainly is going to need a closet. But
what kind of closet? Sliding door, bi-fold doors, swing door?

Are the doors going to be smooth or do you want a raised panel
door? How long will the closet be, how deep will it be? What kind of
shelving do you want?

See how much you have to think about? And I'm only talking about
a closet. And we haven't finished that yet. 

If you want to see how it is done by yourself then read anyone of my ebooks.
You can learn about them here.