As with everything around here, "it depends..."
Usually I'll build 50 more than I need for whatever is coming up, and how much time I have available to invest in my reloading process between matches. For back-to-back shooting weekends I'll usually work an hour or so a few days in a row the week before and spread out the process so the wife doesn't get mad because I spent an entire weekend down in the shop reloading. I try not to let things go to where I'm down to less than 100 cases that haven't begun my reloading process yet. That's when it becomes a chore working on 700-800 pieces of brass through the entire process and it gets boring fast.
Most of the time, within a day of coming home from a match I'll start the process for that brass, so it's just a steady rotation of fired-not-cleaned, cleaned-not-sized, sized-not-cleaned, ready-to-load, and finished rounds.