stir plate build

I am going to start to build a stir plate... I have most parts that I think I need: a housing(height-4 inches, width/length-8 inches), rheostat, computer fan, 5 volt power adapter, on/off switch.
I would like to know if it matters on what type of magnets to use? Most I have seen use magnets from computer hard drives, but I have a few different types on hand. Does it really matter with the magnets? Would appreciate the help.

It needs to be a rare earth magnet. Very powerful, otherwise it won't be able to attract the stir bar.

That's not a problem then. I have quite a few rare earth magnets from work in various sizes. Thanks for the input.