I would suggest that you stop and think about exactly what you are trying to achieve
As TONE has said - are the songs finished songs that you want to sound "better" - or are they ideas that you want to be expanded?
What exactly do you want the producer to do for you?
Are you paying the producer/company a fee?
The protocol from my experience is:
Rough Demo - this is the bones of the track to ensure the song "works" - often with just guitar/vocal or piano/vocal - possibly recorded on a phone etc.
The days of sending a "rough demo" to a publisher/record company and expecting them to imagine what the full produced version would sound like are long gone (IMHO) as you will be competing against fully produced "radio ready" demos
If you are using a producer to turn your "rough demo" into something ready to send to a publisher/record company then I would expect to pay a fee for this service and you would need to explain in full to the producer what you expect
There are many companies that offer this service and the one TONE used recently sounded top notch - both the quality of the finished product and their general approach
Be very clear about any "writing credits" - eg if the producer adds a melodic hook does he get a share of the writing credits?
It does sound like you want to give the producer a "bag of parts" to build the song - I could see this getting quite expensive (writing time, session musicians, studio time etc.) if it is not a non-paid for collaboration so please be careful and get a full, up front, all inclusive cost