Take a length measurement and a width measurement of you existing metal stand.
get some 1/4 inch finish playwood ... one side will be rough the other side will look nice with wood grains and such.
Also get sone 2x4's. You can always take back what you dont use. I would get 8' lengths of 2X4.
First cut some small 2X4 pieces for shims 6" pieces would work.Place one in all 8 sides where the corners are.
Place one 2X4 on the bottom back side of your stand so its sitting on the floor and one in the front same way . You want them so the 4 inch side is vertical. Measure the distance between the boards this will make your bottom side pieces.
Get those cut and put them in place, then mark the front and back boards so that your line is flush with the face of the side boards. That will give you your base. I would also put a board in the middle spanning the front to back to sturdy it up.
next remove the shims you made and measre to the top of the stand from the floor. that will give you your riser pieces. these pieces go in the corners you need 2 pieces on in the front left corner and front side corner so they meet and so on for other corners.
Then you make a box for the top by measuring across the fron sides ect like the bottom one you made and your ready to add the finished plywood panels. you can frame out doors in the fron ams leave the back panelless . its not that tough but if you have a corless drill/driver , combination miter saw , and a tape measure its easy as pie ive made up a good dozen of them for myself and firends.