I think everyone has thought about this once or twice, thinking how awesome it would be to create your own ship. However, there are problems associated with this:
1) This kind of feature would be very "expensive" in terms of space. It would definitely make the game run slower and would make the overall experience less enjoyable.
2) Do you really want to see stupid looking ships in your battle tab?

There are bound to be some. I personally like the look of existing ships.
3) This kind of feature will take up a LOT of developer time and energy. He could be spending it on more functional and less "razzle-dazzle" type things. I know there are a lot more things I'd much rather have than a ship creating ability.
Overall, I think it would be a cool idea, but not really that doable.
-1 from me.