This instructable details how I made a UFO out of cardboard, foil, Christmas lights and duct tape for my front yard last year.

Items you'll need:
Several large sections of cardboard (I used 3 or 4)
Christmas lights (I used 2 separate strands of chasers)
Aluminum foil (heavy duty works best)
Thin wooden dowels
Plenty of duct tape
Spray on glue if you have it (plain white if you don't--just go thin)
Glow in the dark paint
Extension cord(s)

Tools:
X-acto knife
Putty spreader / bowl scraper
Nail set punch that's a bit smaller in diameter than your lights
Small screw and string
Sharpie marker
Hot glue gun (for dome top)

Extras:
Plastic candy bowls (to make the dome top)
Caution tape
CD Player and CD of alien crash sounds
Fog machine
Dead alien
Black light

Step 1: The Plan

You can see at center-left of the page the 2-pie-tins shape. This is actually going to be a top and bottom disc joined by 8 "wings" duct taped together, with a support piece in the middle for rigidity and strength.

The cone shapes on the right side were supposed to be the top of the saucer, but it never came together.

This thing requires 3 or 4 large sheets of cardboard.

I scrounged some from packaging for several big mark boards that were ordered at my office. Other places to look include furniture stores and appliance stores.

Step 2: Make the Top and Bottom

Lay out your cardboard and find a center point for your circle. Try to avoid creases or folds as they weaken the structure of corrugated cb.

Tie some string to a small screw and your marker. Snug the screw into the cb and trace the circle with the marker.

Cut out with xacto knife. Make 2 circles.

Step 3: Make the Center Support and Join to Top and Bottom

Cut out 2 rectangles that are about as long as the diameter of the circles from step 2 (mine were a bit short, which was ok). Make sure to cut so the grain runs in the short axis.

Cut a notch at the middle of each to the halfway point.

Cut out pass-thru holes on either side of the notch.

Slide the pieces together so they form an "X" shaped support.

Duct-tape the joint so it doesn't slide around.

Use the nail holes in the top and bottom circles to align the support to center and duct tape into place.

Step 4: Make the Wings

The wings take time to make because there are so many pieces.

I cut out 16 identically-sized rectangles from one of the other large pieces of cardboard. They were about 16" long and 14" wide. But these dimensions are up to you.

Tape 2 rectangles together edge-to-edge on the short edges to make 1 wing panel. Repeat to make 8 wing panels.

On the "top" of each complete wing panel, mark spots using a template. I made mine in Paint Shop Pro and printed on card stock I had handy. Pentagons are spacey, but you can use any shape.

Step 5: Tape on the Wings and Make a Light Pattern on the Top

Duct tape the wing panels to the top and bottom discs in an octagon shape. Don't worry about the gaps between the panels, we will cover the spaces later.

Lay out a pattern for the saucer top lights and punch them out.

I used the same nail-and-string method for drawing the concentric circles for my saucer top.

Step 6: Foil, Lights, Sticks and Paint

This part is tedious. Use the spray glue (or a thin layer of Elmer's) to adhere the foil to the deck and wings. Use the spreader to smooth down the foil. Don't worry if the foil gets crumpled--it's a crash site.

Go ahead at this step and push the lights thru the pre-punched holes for both the deck and wings. The foil will help hold them in position. Use the pass thrus you cut out earlier to run the cables. I also had to duct tape the lights to the underside of the UFO in a few places.

(No pics of this step--sorry) To cover the spaces between the wing panels, cut dowels to fit between the wing panels and tape them down at the corners. Then drape a sheet of foil over the space and glue down to the adjacent wings.

Use glow in the dark paint to make alien glyphs and markings on your craft. I used a blacklight to make the letters glow bright.

The dome was made from 2 plastic candy bowls I sprayed silver and hot-glued together. Then I hot glued the assembly to the top deck.

Step 7: Stage Your Crash

I taped off a section of my front yard and set the UFO on a tree stump. I had a fog machine on remote control tucked up inside the UFO. Since half the bottom is exposed, the fog billowed out nicely. I also made a continuous automated alien distress signal CD and tucked it up in the ship next to the fog machine.

I had some leftover cardboard, foil and paint, so I made random bits of flotsom and jetsom.

My wife made the alien from an old track suit stuffed with newspaper, some latex exam gloves full of flour slurry and glow paint, and a small pumpkin painted up to glow.

Out of frame is my black light attached to that white extension cord.

Step 8: Sound Effects

I created a CD of sound effects for the crash site. Basically a continuous play of an mp3 I put together from pieces I found on the Internet. You're welcome to use it if you like.