Question
what is the standard slope of college baseball field

Answer
The standard OUTFIELD slope is no less than 1% slope (1" per foot), no greater than 2 1/2% (3-1/4" per foot) slope away from the Diamond.  There are three ways to accomplish this.  One is to slope the grade away to out-field, or create a ridge from 2nd base to center outfield with the slopes falling to 1st and 3rd. The third way is to make a high point at middle center field and use a low, flat swale with the high point just past 2nd base, and a gentle drop in either direction just beyond the 1st and 3rd bases. (Again, using the 1% to 2-1/2% slope range)

The infield is a little different. For a skinned in field, you drain it away from the pitcher's mound (the high point - about 7" to 8" higher than 1st and 3rd) in all directions at 1%.  

Its best to use a sub-drain thoughout.  We really don't get enough rain here to worry about soggy fields, but its good professional practice to do so.  The local folks here usually cut that item from the budget, but we show it on our plans anyway (Hey, let the client make the decision to axe this critical item).

I'm sure there is an official NCAA guideline that just contradicted everything I just wrote.  So, if I were designing a field for a Division-level team, I'd contact the NCAA, first.

If you want to just build a recreational field, here is a link with the basics: http://www.baseballfielddesign.com/

With a grassy, multi-use, park-like field all bets are off.  The maintainance guy mowing the lawn doesn't want to have to slow down for a pitcher's mound, so its usually graded at a constant cross-slope (again from 1% to 2-1/2% max).

Hope it helps.