You have to understand that there is no rule or formula which states that you should build a specific number of production buildings for workers in this game. Just like everything else in this game, it will never be that easy. Population limits as well as the fact that you happen to be human will make it possible for you to get involved in the acting of floating. The number of production structures that you have will determine whether you will make use of it or not. For instance, production structures which are surplus can only imply that less cash will be used. On the other hand, if you have only one, you may be required to build more as time goes on.
It is better to have lots of structures than just one or few of them. There is a trick which you should always remember. This is avoiding the act of sacrificing your resources for the building of too many tech buildings or production structures. It is always difficult trying to arrive at the number of production structures which are necessary for you to build. This is due to the fact that the various units don’t have a similar ration when compared to mineral cost and gas. For training purposes, below are some estimates for one mineral field.
Terran
Protoss
Zerg
Practicing Time
Having seen the suggestions above, it is high time you started practising. This is one stage where even the experts usually struggle. The major key here is to avoid practising in a sandbox all by yourself. Rather, what you should be aiming to do is play against an opponent that seems better and more experienced than you are.
Playing against a weaker opponent prevents you from multitasking effectively. Secondly, it may seem easier spending money which isn’t in the real sense. When playing against an experienced opponent, you will hardly have time for training of units in a way that is not interrupted. This is because you will likely be doing different things at once. These could be scouting, combating, building, expanding, unit upgrading and lots more. There are lots of distractions which you may have to deal with when playing against an experienced player. A player that is weak will bring about complacency in you.