I had this scene in my haunt for a couple of years. I used aliens that I got from the state fair, they are 4' blow up aliens and are all different colors, then I made a space ship using paper mache'.
Here are the instructions on how to make the space ship using paper mache'
I took on old round snow sled (about 3' diameter), put saran wrap over it and paper mache'd over it making the end that hangs down about 1 foot long. I did this twice to make 2 pieces. Then I glued the pieces together sliding the ends that hung down into one another, then after the glue dried, I cut 4" in diameter circles all around the center and spray painted the whole thing inside and out with chrome spray paint, then glued colored saran wrap (on the inside)over the circles I cut out, leaving one with just the top part of the saran wrap glued so I could get my hand inside of the ship. I would then glue fishing line to the tip or cut a hole for it to loop and tie it. Finally, place a strand of multi color and multi function christmas lights inside. Looks really cool when it changes color! That's it,, your done!
You can put a colored light up party ball in your alien scene for extra light and color, fog is cool in this scene as well.