First of this not really a guide to team building more of a peice of advice or information. Keep in mind you don't have to use the following methods i post its your choice i am only giving you some advice on what team building is all about. So Lets get started.
First things first some of you i know like to start with the lead Pokemon then follow it from there. I find this method still very effective alllows you to pick any lead you wish to use and effective put a team together based on that lead. However i like to start with the following. I see whats being most ubused in the metagame examples like scizor,latias,tyranitar etc you get the point. Based on the most abused Pokemon i like to start by placing a counter for those kinda Pokemon right off the bat. This allows you to take care of potential treats right off the bat wiithout doing major fixing after testing it out it also allows you too find Pokemon that syncs together with the counter. After you fill in the potential threats you might have with the metagame you start to fill in the walls special sweepers and so on, but make sure that it syncs with the rest or else you are wasting your time. After chosing all those picl the lead that best fit the team i find easy picking the lead last as it alloows me too see what best fit the team i end up making. Team building is about keeping the team in sync with each other without sync any team will fall apart. Of course chosing the right Pokemon are also important, but keeping the sync comes first.
thats not really a guide just a piece of advice sharing with you all. Oh i forgot to mention something before even starting to pick any Pokemon keep in mind what sort of type team you are building knowing before hand will allow you to chose the best options out there.
