I don't understand, as planets are made from asteroids. Of course, if you mad ea planet out of an asteroid fields, and it ends up bieng gas or ice, then the none planet based lifeforms would be able to colonize them.
Perhaps with create planet the basic could be a noen atmosphere - an additional technology type on board could be create planet atmosphere component that could 1st level of tech random atmosphere and 2nd level tech could be the choice of actual atmostphere.