When I build a team I just try to make sure the team covers its own weaknesses. Beldum Labs synergy calculator is great for defensive synergy. and from an offensive standpoint i basically test things out and see if i have trouble with a certain poke, and if i do i find a viable replacement. If I'm serious about it I might even make a checklist of the top 30 pokes on the usage statistics. But in general if your team supports itself its gonna fair pretty well.