Total Darkness setup...on a budget

This setup will provide total darkness from dusk to dawn, and can't see the edges of my fingers or the blades of the ceiling fan darkness at noon. And is totally and everyday reversible, to any desired light level, on demand. If you live with someone this setup should allieviate complaints about appearances since your existing window curtains should hide everything after you're done. I have old vertical glide-style windows; newer windows are more compatible with modern in-window-frame blackout blinds which are rather expensive and still require an additional layer of blackout curtain which will also leak light on all the sides.

My setup works with any style window that has a sill (more or stronger magnets might be needed with no sill), and keeps light leakage to the absolute minimum. And you only have to do this once! Any future repairs should be simple and quick. Total cost for two windows is around $85-$95, it would be at least $200-$250 for the pre-made options.

Materials:

RYB HOME Self Sticky Blackout Window Curtain https://www.amazon.com/dp/B07F2RLBPR/ref=cm_sw_r_cp_apa_i_fN0kDbWM5TSG3 $10 per curtain on Amazon, make sure they're the style with the zipper. Don't get the linen ones, they look like they might transmit too much light. Measure your windows.

Coroplast - $5 at Michael's Crafts, 20x30, at least 5 of them, opaque (hold it up to the ceiling lights to check) black corrugated plastic cardboard. It's often used to make yard sale signs since it's weather-proof. They didn't have it at Staples or Home Depot. This stuff won't get wet, stay wet, and grow black mold like cardboard will in cold climates during winter. And it's durable.

Flexible Magnetic Strip - 1/2 Inch https://www.amazon.com/dp/B078SVG2CC/ref=cm_sw_r_cp_apa_i_6P0kDbEK9AFEJ $11, I don't know if they currently carry it at Home Depot. I used the 1/2 inch wide stock. If you can find a few stronger (bit thicker) magnets, such as from the backs of refrigerator ones you may need them later if the panels wind-up not magnetically contacting with enough strength in a few of the anchor-spots.

E6000 Adhesive - $5 at Home Depot. Don't use two-part epoxy on the Coroplast, I did a test piece and the parts came apart after 3 days of use. E6000 is flexible, but takes at least 24 hours to cure before use.

J-B Weld Epoxy (two-part) - $5 at Home Depot, get two. The JB weld brand has a patented no-mess cap that is sooo good, and it doesn't cost extra. You'll use this to glue the metal pieces to the wall around the window frame, as well as the velcro for the zippered blackout curtains.

Switch Box Supports https://www.homedepot.com/p/RACO-Old-Work-Switch-Box-Supports-25-Pack-8977/202956471 72 cents each in the electrical section of Home Depot, get at least six to cut up into 24 equal sized pieces. If you can get larger stock of a thin metal (must be steel for the magnets!) you can cut with tin snips, all the better.

Painters Tape, Clothespins (a bunch), Scrap Cardboard cut up into little pieces 2 in x 2 in or so, Tin Snips, Screw Driver, at least 4 screws and 4 washers (for 2 windows), Drill or hole punch, Utility Razor Knife, Straight Edge (metal or otherwise), misc. smallish weights (anything really) to keep pieces in contact while curing, pack of Hair Pins ($1.50, they used to be called Bobby Pins, but were labled Roller Pins or Pinup Pins at Walmart), 4 small plastic picture or bathroom wall hooks to anchor the curtains elastic-loop retaining bands to.

First, the Coroplast likely won't be wide enough for your windows, so take the fifth piece and cut it into 8 equal-width pieces to make extending wing pieces that will let each of the 4 panels you'll be making extend and inch or so beyond the window frames. You'll need some floor or table space, since the panels need to cure while flat after glue-up. Use the smallish misc. weights to keep the wing pieces in firm contact. Wing pieces on the table/floor, panel piece atop with the weights places along the contact edge.

You can work in stages, and glue at least three 1 & 1/2 inch pieces of the magnetic tape along each side of the panels with the E6000 (not the two-part epoxy!). My magnetic tape was old and the adhesive was shot, so I can't attest to the strength of the adhesive on new stock. Use the little pieces of cardboard along with the clothespins to keep them in contact while they dry. I found the clothespins stuck to the magnets and were harder to remove than the cardboard. It also spread out the pressure.

Also when I cut down the height of the other 4 pieces of Coroplast by an inch and a quarter or so, I saved those 30 inch long pieces to glue onto the front bottom edge of the top panel to block the light from the gap where the upper and lower panels meet-up. I also had 4 smaller 1/2 inch by 1 inch or so pieces of Coroplast that I glued onto the back-bottom-edge of the top panels, spaced-apart, with a couple of pieces of thicker non-corrugated cardboard under them to give some space to make it easier to guide the top panel onto the bottom one and keep them snugly and light-tight together.

You can glue a couple of the clothespins together to make some handles to grab when removing the top panels. But don't epoxy them on, they will fall off! Drill four holes in the Coroplast and one into each clothespin handle, and screw them on with a washer on the back to spread the pressure out.

Next step is to make some marks on your wall where you want the velcro for the curtains to lay, at least 2-3 inches outside the perimeter of your window frames. Work in stages since the stuff dries way too quickly, and spread a moderate amount of the two-part epoxy both on the wall and on the velcro before pressing it on. Find a large piece of flat cardboard and pin the Velcro strips down, this makes it a lot easier to manage the epoxy application. You shoudln't need tape to keep it up while drying because of the surface area involved. Make sure the velcro meets up with no gaps in the corners. Don't rely on the sticky that comes on the Velcro, IT WILL NOT HOLD.

Last step is to glue those 24 pieces of metal to the wall surrounding the window frames. You'll need to put the panels up and mark where the magnets fall to place them properly, unless you had enough magnetic tape and metal to cover the entire perimeter of the window frame. Use thin strips of painter's tape to hold the pieces to the wall while they dry. Good time to epoxy the plastic hooks too, horizontally oriented and slightly outside the perimeter of the curtain-velcro.

Those Hair Pins are to gather up and hold the slack along the top and bottom of the curtains to minimize light leaks. Paper clips seemed to abraid and dig into the curtain fabric.

You can make your own aluminum tape by layering foil between standard masking/painter's tape to block light around the door jam, and a rolled-up towel will block the light from the bottom.

Also, sticking a bit of black duct tape on the upper corners of the top panel keeps it from digging-into and potentially putting an eventual hole in the fabric of the velcro-curtains.

Edit: Get an extra pair of the steel switch box supports and cut two 5 inch pieces of magnetic tape to glue with E6000 to the center of the top-edge of the outfacing side of both top panels. This reduces the ceiling-bound light leakage even further.