Depending on your definition of "raw materials" the 4th level spell Fabricate (pg. 239 of PHB) might be of use. It only takes 10 minutes to cast.

You convert raw materials into products of the same material.

I see 2 ways that this spell could be used to serve your purpose, given that you have an open-minded GM.

1. On the Flesh - Use Fabricate just on the flesh to make nice furniture (or other products) made out of flesh in a different space away from the body. This method should leave the skeleton behind. This might be a too liberal use of the term "raw materials", however it does say in its description that works on organic material.
2. On the Bones - Use Fabricate on the bones to recreate the skeleton in a different space. Bone might considered more raw material than flesh. However, since you have to see the material, you'd need to slice up the body quite a bit to see all the bones requiring more time. Though here's a benefit, if you just had time to gather one bone at a time, you could use an assortment of bones to make a full skeleton at a later time. Also, you could make small-sized skeletons this way if so desired.

As an added note, I'm using this question here to justify that Fabricate's no-creature condition would work in this case: Is a dead creature's body considered an “object”?

They can, but it's up to the DM whether they're proficient

Rules designer Jeremy Crawford unofficially addresses this here on Twitter (in a manner of speaking):

Twitter user: can I give the undead I create with Animate Dead weapons and/or armor?

Crawford: You can dress up your undead thralls however you like!

Twitter user: nice! As long as they're proficient I assume…?

Crawford: Undead dress-up dolls can wear anything, but they suffer the normal consequences if they're not proficient.

Of course, this doesn't say whether undead are inherently proficient or not with any armor or weapons you give them. That's probably a DM decision. If you're turning dead party members into undead minions or something, they might retain their proficiencies from when they were alive.

Fellow designer Mike Mearls also provides his own unofficial opinion as a DM here:

Twitter user: I can't find anything official on wether skeletons and zombies are proficient with armor and weapons given by a necromancer

Mearls: i'd give them proficiency with all armor and weapons

Of course, this isn't actually an official ruling in any way, just Mearls' own opinion.

If you're the DM, you should consider what changing their equipment and proficiencies does to their CR and how it might affect encounters.

If you're a player who wants to do this, you should probably run it by your DM, because it's largely up to them whether they'll allow this and whether the undead would retain their proficiencies.