Custom orders are not something I offer very often and I am very selective regarding what I'm willing to make and the time it'll take.
Understand that my willingness is based on many factors, including time, availability, interest in the work being requested, amount of time the requester needs in back-and-forth dialog to get the piece requested (if we spend 5 hours back and forth, that's time and money not making), etc. 30 minutes in back-and-forth dialog total is fair. It is important you know what you want, have thought it through. If you wish for me to create an entirely new design (or are very particular) and it is something I'm interested in creating for you, please know that time beyond 30 minutes will be billed on the piece's final price at $20/hour (this is less than half of my hourly cost for making, but provides me with a way to recover worktime, financially).
Most custom orders for pieces that are already in my repertoire are usually not an issue.
Please never ask me to create something that another maker creates. Botanicals aren't owned by artists but- though there is ample creative theft in the online world- I will never accept work to create a piece based on another's designs. I feel strongly that all work should be original and that integrity in one's work requires active and honest internal dialog. Rather than, "how many elements of this person's work is it ok to use without stealing their design?" I opt for, "this is someone else's element, I will not use it."
If you have a design in mind that is not within my area, please feel free to ask me if I know another artist who makes similar pieces. While there is no way I can speak for that artist, finding the right artist, one who makes what you're dreaming up makes more sense than asking me to make something that isn't in my range. And, to be honest, work that is forced never turns out as well.
It never hurts to ask. Worst case, I say "no." Best case, I make it. Middle of the road, I don't make it but know someone who will.