If you're looking for manga similar to Zoids: New Century, you might like these titles.
Ten years ago, Tatsuya Yuuki befriended a boy who taught him all about Gunpla and battling. This is the story about the GBF world back then, showing Tatsuya’s story and progression as an amazing builder and fighter!
Perverted, cocky Ken used to live a normal life until several giant monsters crashed onto his city. In the midst of their carnage Ken’s secret crush was killed, and his grandfather seriously injured. Hope seemed lost for the inhabitants of the city and the world, until Ken discovered that he holds the key to summon the pilotable Beast-God Riger! Within the massive bio armor, Ken must now battle the invading monsters to protect Earth, and keep them from awakening a demon within the Demon Stone – a demon who will put a stop to all human life for good!
When a great fleet of flying saucers invades Earth, it awakens the true power of Daisuke Uryuu.