Yes, it does work that way. I purchased it years ago from my local camper supply dealer. I noticed when I did a search of Google and Camping World that the models they sell now don't have the handle at the top to pull, instead they have a pin to pull out that allows them to drop down. Go to Camping World or search Amazon and you can find this type.
MikeB

I made the top out of 2x6 sides, front board, back board, and 1/4" plywood for the top and bottom. It measures 6" deep x 42" wide x 68" long. The top was reinforced with 1x1 boards glued across every two feet with the sides and back board made from 1x2 1/2" boards. I used a piano hinge across the front. As you can see from the picture below I used simple boards to support it when it was open, but attached a chain and spring to prevent the wind from catching it and flipping it open. The little black rectangle on the lid is an LED light to see what I am doing or getting at night. The bottom was also made of 1/4" plywood with 2x2's reinforcing it every two feet.
https://blazerforum.com/forum/attach...ine=1412279798

For it to fit on my roof rack, I had to make some box inserts for the crossbars of my roof rack. I used 1" boards to make these as illustrated by the next picture.
https://blazerforum.com/forum/attach...ine=1412280377

In the next picture, you an see the 1x1 reinforcements for the top plywood, the 2x2 reinforcements for the bottom plywood, and the box enclosure for the roof rack. Ignore the boards inbetween the 2x2 and box enclosure as that was a replacement box enclosure that I covered over for the previous pickup topper I used it on. (It has gone through two remodels already and been repainted several times.
https://blazerforum.com/forum/attach...ine=1412281076

Here is an outside picture of my roof rack box enclosure. If you have an adjustable roof rack, you could put your bars at the front and back of your box and not have to builds the box enclosures like I did. But the old roof rack on my 1990 Blazer is not adjustable.
http://abe.midco.net/~barondeau1/Vettes/CIMG0101a.JPG

As you can see in the above picture, I used my router to route out a space for the top sides in the 2x6 sides of the main box for a flush fit. I did not do that at the back edge. The front of the box was cut at an angle for cutting wind resistance and is just a fake hollow space underneath as seen in the next picture. The metal eyebolts are for anchoring my blue rain tarp when I set it up. Also use the eyebolts to hoist it up off the Blazer for storage. I hang it from my garage ceiling in the winter time.
http://abe.midco.net/~barondeau1/Vettes/CIMG0104a.JPG

I hope some of this information gives you help and ideas for making your own box on top of your Blazer. It does not look like it will hold a lot with it being only 6" deep, but you would be surprized how much stuff I can get stored up there. I generally carry my tent, camp stove, portable toilet, spare propane tanks, spare batteries, spare plastic bags, blue rain tarp, plastic ground cloth, bag of tools and connectors, window screens, umbrella top, and camera tripod up there. The truck tire step mentioned in posting #6 allows me to access everything in the box from either side of the vehicle. Feel free to contact me for more information on anything or if you would like a more detailed picture of any part.

To give you a better idea of the umbrella I made for my portable picnic table to use under the blue tarp for support, as I mentioned in posting #16 here is a picture of the parts dismantled. The metal pieces are for holding magnetic LED trouble lights.
https://blazerforum.com/forum/attach...ine=1412281578

Here is a better picture of the spare tire holder mentioned in posting #17. I had my local welder, weld a flat plate on the back of my tray support to bolt it on with. It does fold down for easier access to my boxed supplies.
https://blazerforum.com/forum/attach...ine=1412281755

The space at the back of the mattress on either side was also utilized. I built a small box on the right side with space underneath for storing a spare blanket. Behind it sits the angled shelf I made for the bucket holding our shower flip-flops. To the left of the bucket is the black tire step all folded up and stored on the edge of the mattress. (I mentioned in posting # 6 that I would show a better picture of its storage space.) On top of the spare blanket box we use a red canvas bag that we got at a Pier 1 type of imports store for storing towels and other clothing. We use 4 of those same type of canvas bags to divide up our stored materials in the big black box on the back of the tray, too.
https://blazerforum.com/forum/attach...ine=1412282143
https://blazerforum.com/forum/attach...ine=1412347941

For storage on the left side of the mattress, we found a plastic white waste basket that fit very nicely for storing, coats, extra sweatshirts, hiking hats, etc. In front of it, we store our hiking boots. Nothing fancy here.
http://abe.midco.net/~barondeau1/Vettes/DSC_0906a.JPG

Wow, thanks for the pics. Lots of detail! I'm actually about to go with a roof basket, but it never occurred to me to build one out of wood. (And I work in a Lumberyard. DOH!) It looks GREAT! I can tell you put a lot of thought and work into constructing it. And I'm sure it's very functional.

When I was looking for storage space for my roof rack, all the commercial units were so high and created a lot of wind resistance, so I decided to try and make my own in a low, wide profile to hopefully cut down the wind resistance. I still make 15-16 miles per gallon with my 1990 Blazer which is not much worse than when I didn't have the box on top. It doesn't look like it, but it can hold a tremendous amound of stuff up there. I used to remove it with a pulley and winch system in my garage every winter, but now that I am retired and still go south camping during the winter, I leave it on the Blazer full time.