Did a similar thing, just instead of using composite board went instead for cheap C grade shutterply, and to make things even easier just had the boards cut at the supplier. Used a single dimension cut, so the whole 2440 x 1220 sheet was cut at 300mm increments so I had a whole load of 1220 by 300mm sheets, plus one slightly larger that became the top. Then simply spent some time using wood glue and a lot of long drywall and chipboard screws, plus the drill and some sacrificial bits, to put in all the screws to give a shelf unit to use. Some are 4 layer, some are 3 layer, as this fits the boxes I use in them, and this gives a good range of possibilities, just added a brace on the back to make it more sturdy, as buying a full sheet of the shutterply just to act as backing was going to double the cost, and those boards are not cheap, but a whole lot stronger than the shyteboard.
Sand and then a coat of finish made them look more appealing, and making more is easy.
For those units Dave has I would recommend using glue on the joints, and making the shelves a permanent fix with some chipboard screws and glue, as this will make it more robust. The rear brace also is needed. Use longer screws than supplied, the longest you can get, probably a 60mm one, as the board strength is poor, especially near the edges, and the long screws spread the loading out over a larger area of the board, so it is less likely to tear and delaminate with shock of load.
At least put the base of the feet on, as this will keep the shelving units from wicking up moisture from the floor in the event of a spill, which will cause the chipboard to rapidly turn into powder, as the modern stuff is formaldehyde free, and thus is very sensitive to moisture. the only chipboard that is still formaldehyde based is that meant for marine applications, where they still use the impregnation with formaldehyde glue and high pressure and heat for curing, to get a product that will actually survive immersion is sea water for a few hours without failure. Expensive though, and not many plants left that make it, the one inland closed down a few years ago, kind of sad as my father did a lot of the construction and plant works there when they opened the plant a half century ago.