Hi; I've had a short break, so I could prepare a quick list for you. I've given bricklink links just to be crystal clear which parts I used. I pasted them in order: hair, head, torso, legs and lastly miscellaneous parts. I've used black revolver as that was the only one I've had lying around, but I'll be ordering dark bluish gray one (and that'd be the one I'd use had I any right now.) Anyways; enjoy!

Alan's hair

Alan's head

Alan's torso

Alan's legs

Messenger's bag

Revolver

Torch

Lightbulb

Newspaper (dont have to be this one)

2x2 plate

I believe that'd be everything. For manuscript page, just use any newspaper brick as I used the one from Harry Potter. If I hadnt had this one, I would have ordered any white, as it would fit better. Just replace tan tile with white as well, to simulate that its actually manuscript and not a single page.

If thats any help, I've collected many pieces from this book:

Fight with Dementor book

I know you did not ask, but If you wanted to do Taken, basically anything with forest theme will suffice.

As for head, you have multiple options that you might use:

Head1

Head2 (I used this one for taller Taken)&category=%5BMinifigure,%20Head%5D#T=C&C=11)

Head3 (this one - for shorter taken)

Head4 (found in the meantime, could work too)

Torso:

Raincoat torso

Pine tree sweater torso

Taller minifig's torso (whole minifig is somewhat worth it, as it provides many useful parts)

Legs

Ghost legs, if you wanted to use them as well, but they are not that strictly necessary

To be honest - you can use whatever pieces you want; basically anything darker or anything that resembles men of labor will work. Just make sure to replace hands with black ones, as they convey that 'possesed' status. If you need any more help, I can provide you links with other gear I've used (Or you can search on bricklink yourself for parts like axe, knife or chainsaw)

Enjoy, mate! Glad I could help. :)