We don't budget for individual items anymore. I've figured out most of the infrequent recurring costs and they are now part of the budget. The money for the car, new roof, etc is piled in with everything else. Yes, if you've got a really big expense coming up (e.g. college costs) it probably makes sense to separate that into a low-risk bin (e.g. CD's or a MM fund). But once you take a look at all these expenses (new roof, appliance replacements, cars, house painting, etc) they add up to a fairly big pile and can be thought of as fairly regular occurrences, on average. If you set aside all the money you'd need to cover all of them in a low-growth safe account "just in case," you'd be forfeiting a lot of growth.
a thread we did recently on some typical expenses. I still need to organize it. Rich in Tampa also started a thread similar to yours some time previous to that, here