It will depends on your project, ILuv3ggs... In a lot of cases, it is possible to re-use wheels from another kit, sometimes straight from the box, sometimes with a bit of conversion. So check out your drawings and pics and look out (or ask here) for existing parts that 'fit the bill'.
For instance, I have been thinking of scratchbuilding the Korean K1 MBT (1/72), and the wheels and tracks can easily be adapted from the M1 Abrams.
In some cases, you will not find a close 'donor' model, so that's when you'd need to scratch a very good copy of one wheel and cast the others in resin. I'll then use anything 'handy' to help... plastic or metal tubing, plasticard, buttons, wheels from other kits, sections of pens, ...
In a lot of modern armor, skirts hide the wheels or a large part of them (return rollers in particular) and this will help you a bit (no need to model what you don't see!).