get an explorer as the very first thing to do. fly to your opponents
base and order a wall to be built around his 1st swarm. reduce workers
to 0 for all these walls and have an eye on upcoming swarms.
now _that_ is a cheap trick isn't it?
Greetings, Leo
P.S.: this should not be like that! buildings not yet being built should
neither block opponents nore resources. we need to make the globs free
the area themselfes so you don't have to care about resources when you
place or upgrade a building. clearing is part of the job of building.