Are you getting it delivered from a regular coalman?
How wide is the porch?
Need more info and if you post pics I can tell you exactly what to do. For example If the porch is less than 6 foot wide, you have access under it, there is enough to get even few degrees of pitch on the chute from the edge of the porch to the window and you're getting it delivered by a coalman with a regular coal truck you don't have to do anything.
Specify the coal size too as that makes a difference.
The chute itself if you need one can be made of anything for support. you'll have to line it with something like aluminum, vinyl sheeting like the thickness of vinyl siding. If you use metal stick with aluminum or stainless. For your situation even some scrap siding will be ok because its not going to get the use.
Generally the best thing to do with a porch is cut a trap door where the window is and throw a carpet over it but that really depends on your situation. Like I said post a picture and I can provide better info.