I know, a lot of people have made their own version. So i had to have mine as well. Lol! Had to start somewhere. A quick sketch of the important info I needed. This build was for my niece Kenzie. She just wanted 3 things. 1 eye, open mouth smile, and squiggly hair. My measurements were her shoulders (widest part), height and how far off the floor to the bottom of the costume. The rest was up to my imagination, tapped abilities and a lot of friends advice. So here we go!

Step 1: Tools and Supplies

I kept tools pretty simple. A rotary cutter, gel pen, sharpie marker, scissors, hot glue gun, heat gun and tape measure.
As for materials; I had some poly foam for another build. It was a 4x6 and half inch thick. A run to Goodwill netted me some yellow and blue cloth, a couple suspenders, pleather belts and a plastic hula hoop.
A run to the fabric store for some mesh cloth (I can't remember its exact name, I'm sorry. It is a fine mesh you can see through. it started with the letter C...)
Art supply store for 2 cans of adhesive spray, fabric markers, and the optional foam letters for the end prop I had to add for her!

Step 2:

Basically, I curled the poly foam around and made sure the inside was 19 inches. Her shoulders were 17 but I wanted her to be able to move around. I cut and trimmed based on the measurements I had (like I said, just needed the basics). Hot glue did a perfect job of sticking everything together.
The mono-goggle was actually the plastic lid to a can of Bondo from any parts store. As you can see, I placed it in various places to get a good idea of where to put it. Held in place by an Allen wrench poked through the center.
The top of the head, I just cut a bunch of slits and folded them down to give it the curve and shape. Then some masking tape added to smooth the look a bit.
Once I was good with where the mouth was, I cut it out. I used scraps to make the teeth.
The last pic was a constant for me, unfortunately. Yes, hot glue is HOT!!

Step 3: Looking Closely Like a Lawsuit...

After cutting all holes out, I used the adhesive spray to stick the yellow cloth to the foam carcass.
More hot glue to fold the cloth into the holes, and a search for more band aids for hot glue that was still HOT! I painted the teeth with basic white auto paint. It cracks but I found white out to be a perfect touch up to keep them pearls shining!
More scrap foam to encase the plastic mono-goggle and the pleather belt for the strap. Hot glue again...
I also had some basic weather stripping sitting around so I added them to the goggle.
I cut the cloth to fit the eye hole, made a few circles and colored them with the fabric markers. More scrap pieces along the inside of the goggle to glue the cloth to and more weather stripping to hide the eye seam.
Blue cloth for the overalls and a simple blue rainbow style arc for the arms.
Added some button studs I saw at the fabric store too that I found. Makes it have the"riveted" look.

Step 4: Hold Up! ..and Other Embellishments.

I took some banding material and made the simple L brackets. I attached the suspenders to the bracket with intent to have the costume rest on those, even though it weighs less than 5 pounds.
I didn't take a pic of it, but on the inside bottom I added the hula hoop. Heat gun and patience got it to shrink down enough to fit into the costume. The brackets just fit into the hoop and it retains its shape.
Hair was just a couple pipe cleaners poked through and bent on the bottom.
Pic 3 looked good but was missing something...
I made a stencil for the GRU symbol. A marker pen and a marker was all that took.

Step 5: A Simple Prop

I just found some foam letters and made a sign. Some adhesive backed letters stuck just fine and hot glue put the board onto a small piece of PVC.
The costume fit her perfectly! She can see through the eye just fine or she can adjust the suspenders and look through the mouth.

As I was leaving my sister house, my niece was still in the costume with my sister and waving and signing at the passing cars! Lol

I know there are plenty of other builds, and this was done differently in some ways. Altogether this build took about 8 hours (first time making one), and about 45 dollars.

Step 6: Last Bit of Words

I had to test fit!
To cut costs, you might want to go thinner with the foam. My half inch foam cost about 30 bucks, but a quarter inch thick ran about 20 or 25. It may need some small PVC to make it more rigid. So the cost may be about the same.
Also, for me it didn't need the extra hoop in the bottom or suspenders, but I did it because I have a couple nieces younger so they can share it. And of course, with kids, they can be a bit rough on stuff, so I made it to last as long as I could.