You will need to do some research to find that several people make these "in their garage" but they're all acceptable and vary in size, shape, quality. I got mine from "SC" (maker's names not state for their legal security) which is not as accurate as MC but better looking than the KS kit.
I didn't need to do a lot of work on it. The assembly took roughly 3 weeks to complete and most of it was spent sewing pieces of velcro to elastic straps.
You will need to spend some time fitting the pieces to your physical build and sand all the edges. Some trimming is necessary so arm yourself with a tough pair of sheers, or a good pair of scissors. Sand paper. A rivet gun, rivets and rivet washers. Some ABS or multi-purpose glue. A sharp, strong "X-acto" knife. Be CAREFUL with this!
Get a heat gun or hair dryer to do some thermo-shaping. The arm pieces will be too wide to sit snuggly around your upper arm and forearms.
For the strap and webbing work, get white thread, black thread, a solid needle, a curbed needle, a thimble. A sewing machine would be nice if you know how to use one (I don't, so I do everything slowly and painfully cause that's how I roll), you can even get outside help.
Roughly put together SC kit.
Chest plates
Most kits will provide you with a two-piece chest armor: back and front plates, which attach together by the shoulder straps and the underarm sides.
Heat-shape them to fit around your ribcage. You don't want your armor to look like it wasn't made for you.
Assembly requires velcro and elastic webbing. Adjust the elastic length to your chest depth, keep in mind that you'll be wearing clothing (flightsuit, cummerbund) underneath. Also leave some room for moving around but not too much.
The back pack of "tank" is assembled with a rivet in the SC kit. But for maximum accuracy you should glue it on to the back plate as there is no rivet on the ABS in the screen costumes.
This is how the tank topper should be painted. You can use decorative decals from auto parts shops for a better result. You can see here that I also painted the rivet in white.
More velcro work to connect the shoulder plates or "bells" to the shoulder straps. The black velcro combo is called a "T-strap". I used a curbed needle to sew the white elastic part to the first piece of velcro, and then sewed the second part of velcro to the white elastic.
They rectangle on the lower left corner is acceptable in black, or gray/off-gray for Lancer status. I used a simple piece of gray duct tape.
Arms & Knees
The Scout Trooper armor kit comes with 6 pieces of arm plates, and 2 knee pads. Their fixations and assembly are pretty straight forward: black/white velcro and black elastic strapping.
You will need to do a bit of heat-shaping on them, and trim/sand certain parts if you're on the small side.
This is the upper-arm piece, comes with a "T-bit" accessory that needs to be glued on, or fixed with a metallic wire through the ABS plate. I did not do that because I'm not confident enough with my drill. You may need to do some sanding on the T-bit, and heat up the plate a little before you place it in. That's a little risky but it worked out fine on this.
Shoulder bells, heat-shaped to narrow them around and trimmed a bit on the lower part. Before and after.
Belt
It's one of the more complex parts of the uniform because it comes as 3 elements: the belt itself, the thigh boxes, the thermal detonator. I suggest you take your time while making it and make sure it fits your hip line and not your waist (if you're female this is important).
You will need a drilling tool (DREMEL or power drill), rivets, rivet gun, rivet washers, sewing needle, thread, etc. Heat-shaping is not necessary but can help if you're really small.
Cutting holes for the thigh box webbing. That's the X-acto knife. I helped myself with my power drill to make a first dent into it. ABS is hard to cut through when it's in an edge or curb. Mind your fingers.
The belt is in one piece in the movie but SC makes it in 3 pieces so we have to stick them together... Some people use glue to avoid using rivets but I would have none of that. Rivets all the way because I suspect a lack of brain cells in the practicality department. Make sure you secure the rivet heads/nibs with foam or cloth to protect your suit.
The thermal detonator, assembled as instructed using glue and zip ties.
It's not completed with it's black greeblies (3 squares and a circle) because I accidentally damaged it with my heatgun, trying to widen the middle strip. Again, brain cell failure. Don't try to heat-shape this piece.
Update: after contacting SC they kindly sent me a new piece of ABS casing, so I eventually was able to redo this part.
Two elements done, now for the thigh boxes.
SC provides you with synthetic white webbing but for screen accuracy (and the Lancer status) you need cotton webbing. It can be white or off-white.
I used the synthetic webbing but replaced it with cotton a week later. I just grabbed an old kimono belt from my Jujitsu days, washed it and got this nice piece of Lancer-material webbing. Recycling is your friend. We scouts love nature, remember that.
To secure your thigh box straps you may want to make something like this, it's velcro, or have pins inside your boxes to adjust the length of your straps. They need to sit rather high on your thighs but I like them just a little lower for comfort.
