Now you'll need a DPS hero to beat the first three boss waves but otherwise this is a pretty safe top build I've seen in-game many times.

Set towers slightly behind the crystal so the towers can cover both top and bottom core.

1. One or Two Tower Boost boost heroes recommended
Note: Hero abilities get forcefully shut off on the last wave... A good way to counter that is to have one boost up(hero boost for example) and wait for it to shut off before activating the next one(tower boost). If you turn on your boost right after it's cooldown it will be shut down, so wait an extra 5 seconds or use the other boost to time when it gets shut off ^^