I was under the impression that it was OP who told police that workmen had been working on his house and had left the ladders there.
So could OP have purposely borrowed the ladders himself that day from Christos and put them there? Therefore, OP will not be able to prove that workmen were there or could it be both?
If it can be proven that ladder/s were intentionally left there by OP or workmen told to leave them there, it will indicate a strong case for premeditation from that time. Otherwise, no one would leave ladders lying around if you were security conscious.
Also if RS had been staying there for a few days, the conflict between OP and RS could have been escalating - hence OP conceived this plan.
It was Christos' ladder, he worked (was working) on the house; he left it. No one else.