Saruman built an army breeding goblins with orcs to make Urukhai and started up forges and training at Isengard as well as improved its defenses. Then to counter Rohan the nearest threat, he built up on pikes and defenses against horses and rallied Dunland men to burn villages and attack people.
Here is my main question. Why didn't Saruman attack the abandoned stronghold of Edoras when he was aware that the main force was at HelmsHelm's Deep?
Once Edoras was captured, he could use it as a fort, and then sally forth to block not attack Helm's Deep until they starved out or escaped through the tunnels in which case he could then take and hold Helms Deep.
It could reward Saruman three strongholds and he could begin to start more breeding pits and training halls with forges at all three.
This seems like a better strategy than storming the walls of Helm's Deep which resulted in his eventual defeat.