From the drum you have a three three possible options
You can get some fairly large size diameter dowel - the benefit is that its already round, the drawback is that you have to find a way to center drill it so that you can mount on you tools. My suggestion would be to use this as a hand sanding tool - cut a length long enough to give you a handle as well as space for attaching the sand paper - good for sanding awkward parts.
If you don't have a lathe this is a relatively quick way to make the sanding drum.
Use a large hole cutting wood bit and drill into a piece of wood ( for deep sanding drums you might have to double up or use a thicker bit - drilling from both sides) this will give you the round drum already with a center hole. The attach a bolt through the center with a large washer on each side of the drum.
Next mount it in you bench drill and sand the drum while it is spinning.
If you have a lathe you don't need to do either of the above. Mount a bit of stock between centers on the lathe and turn it to a drum (sanding as required. If you want to mount it on a drill you can either use the marks left by the lathe centers to drill the enter, or turn a spigot on one end and the remount the piece on the lathe using jaws and once centered drill the center while it it on the lathe.
Note: for drum sanders to be used on bench drill you need to consider the capability of the drill - the sander can not be as large as it would be if used on the lathe
I first of all turned a scrap piece of wood into a drum and then glued sandpaper to it. With the pieces still centred on the lathe this makes an excellent drum sander for small pieces of work where fine control is required. I used this to help finish a hobby horse for my two year old daughter. This idea can also be adapted – by drilling a hole through the centre and securing a bolt through the hole you can mount the sander on a bench drill, if you countersink the head of the bolt it will not interfere with the base of the drill. I used the sander in this format for smoothing a coat hook board (this was a large pieces of MDF and needed to be held flat to the drill base. For both types you could either use a single grade of sandpaper or vary the grades to give a multi purpose device. One word of warning both sanders are reusable, but make sure that you get the centring correct or the vibration can be annoying or possible damage your project.