Step 1: Inspiration
The thing is Tardis is not a box. She is a time machine or rather time travelling creature. Her name means Time And Relative Dimension In Space. She travels with the Doctor, the last of the Time Lords. They travel through time and space, they've been every-where and every-time, they explore and help, they're both very old, but still amazed by the universe. Neil Gaiman called her Doctor's wife. Tardis used to have a feature, that allowed her to adapt her external appearance to the world she landed in, but it broke and she is stuck in the form of English blue police box from the 50s. But Doctor likes it.
"Doctor Who" is the world's longest science-fiction tv show. And it's still in production. Check out the details on wikipedia and start watching now!
I love the show and I really wanted to make a costume connected wit it. I don't like playing the bad characters, Doctor's companion are not distinctive enough, Doctor himself is, hmm, male. But the Tardis is perfect. I wanted to model as many details as possible but also look nice and feminine. So I made a dress.