TARDIS Exterior: "The Amazon Tardis"
Why I went with this design: I wanted to participate in a competition, as I missed the interior one, and decided to get to work thinking of a cool exterior. Unable to come up with any ideas I left it for a few days until one day where I was bored and in the corner of my eye saw my alexa, then some paper, and a pen. 
Images: 

In case you cant read my handwriting:

Tardis trips or 'Deliveries' cost £3.99 per trip. 'Deliveries' are free with: TARDIS PRIME 

It has several voice commands:

• "Tardis, fly to..."
• "Tardis, intruder alert!" 
• "Tardis, lower engine volume"
• "Tardis, purchase prime." 
• "Tardis, sub to poki-" 

and so much more!

The exterior also comes in different colours but I couldn't be bothered drawing them.

#ad 

You may also be happy to know I did not go for the name "TARDWA" (Time and Relative Dimension with Alexa)