Is it okay to ask someone to make a particular fantasy novel? Not a fanfic. I just want to ..
Who will do this?
Ideas are a dime a dozen. A premise or a character is not even a fraction of a fraction of what actually makes the story as a whole to be compelling, which is why writers get annoyed when people ask them to write their ideas like they were providing something innovative or as if it was anything more than a mere writing prompt. The writing is the hard part, not the brainstorming.
1) use a paid writer for this and pay the requested amount - usually based on word count.
can be a ghostwriter or can simply be a commission writer that writes but uses his own name for it.
There are quite a number of people who do this, exactly like any other form of artist or musician.
2) place an idea post at some writer forum and hope that someone within the next five years likes the idea enough to incorporate it into one of his stories.
Biggest problem with that option is that these will usually be writers on the lower end of the quality spectrum, because good writers usually have enough of their own ideas or would go the ghostwriter path and charge you for their work.
3) place the idea into one of your notebooks to store until you have the time and ability to write it yourself.
That is rather common - every even halfway decent writer has more ideas than time to write them. I think I have dozens of dustbunnies in my idea collections, never bothered to count.
Anything else don't bother trying. As said above ideas are cheap, it's the implementation that is the work. And any work of quality has too many requirements to be given without payment.
True I have less time to write and I end up getting lazy before I've written a fraction of my ideas