Sizes? Standard powerpoint slides for standard storyline 3

What is the standard size that a powerpoint should be for a standard storyline 3 course? Sometimes, i have to work with material others have developed and it is already in powerpoint. Importing is sometimes off. I'd like to develop a standard PP template for them to use if they are creating the base/foundation for a training. This will eliminate me having to spend a lot of time reformatting the course.

Any suggestions?