Q about SURGE at Character Creation, How do you determine the # of effects? Options

[de4dmeta1]

OK, so I got Year of the Comet, and I've just read through the SURGE section. I understand how it works and everything, I'm just not sure how you apply it when making a character. Specifically if you opt to spend 5 build points to be affected by it. So here's the question;

If you spend build points to have a character affected by SURGE, how do you determine the severity of the effects?

Normally this is dictated by the number of successes on the SURGE test, but, having paid points to be affected by it, the test wasn't needed. How then do you find what the modifers on the amount of points that go into Positive/Negative effects are? Do you roll and re-roll the test until you succeed, then use however many successes you got then? Or am I completely overlooking something here?