The Combined builder is notoriously known for being one of the worst builder in the game. Meant for it to be "beginner friendly", this race is far from having any sort of balance of holding waves and increasing income. Here is a guide that will help hold your waves while also trying to salvage what little chance of having good income . My best advice: Go greedy, dont waste too much of your gold and resources making combo units and try to tech out of combo, or ECO!
Wave 1: Make an Archer, grab and up mines. If you want to build a High Templar on wave 6 take 2 mana mines in this wave.
Wave 2. Up Mines
Wave 3. Make a Crusader
Wave 4. Make a Crusader, save a zap to zap acid ling
Wave 5. Save a zap to drill big Slimes or incoming sends.
Wave 6. Upgrade Crusader or build a High Templar
Wave 7. Keep Build
Wave 8. Build a High Elf
Wave 9. Keep Build
Wave 10. Build another Crusader