So I am going to start on my first wad....

If you are going to map in GZDoom UDMF map format there is no limit outside of the 64000x64000 map units square where you have to build your map (but it is better to use a 60000x60000 square to avoid strange behaviour). 

To add custom music:

1) since I'm supposing that you are mapping in the MAP01 slot, I will refer to the song name as D_RUNNIN. If you plan to place your map I will provide to you the song name based on the map slot that you are using.

2) download SLADE3 and install it.

3) open SLADE3 and import the desired song in your wad (to do this you simply have to open your wad in SLADE3 and then copy-paste the song inside it, just like in a regular directory). Be sure to use only midi/mus song formats

4) rename the song "D_RUNNIN" (or the name of the song of your map slot)

Some thoughts on your project:

One texture is the best way to have 0 audience. Consider the idea of using a lot of texture but without giving landmarks (like some galleries with wall alcoves, or pillars that exit from the walls). You have to place some detail in your map, but this doesn't mean that your maze is going to be easier to beat (look at Plutonia 2 MAP11 for a perfect example).

Consider the idea of adding height variation (stairs, that bring to hallways, that lead to previously encountered hallways via dropoffs). You have 3 dimensions to build your map, use them all. A maze constructed on more than 1 level is more fascinating (if you have ever played Zelda Breath of the wild you will know his mazes, they are really simple but they have a couple of stairs and tunnels that make them interesting)

Again, if you are able to learn the use of 3D floors you can even add hallways on other hallways, and this adds a lot of complexity to your maze.

You can even use voodoo dolls to change the maze structure in-game (like moving walls, stairs etc.)

Link to the midi list

https://doom.fandom.com/wiki/Doom_II_music

I don't suggest jump straight to gzdoom udmf, especially when you're new and starting mapper. 3d floors, slopes and those all advanced mapping things and actions mean nothing if you don't know about basics like doors, teleports, how actions and tags work and so on. 

So my tips:

1. Study and play maps you like. Open up them in builder and try dissect parts you like.

2. Don't afraid criticism, it will help you improve faster.

3. Ask questions, don't suffer alone. Also search forum - there might be more threads with same answered question. 

On 10/24/2019 at 6:08 PM, I_Punch_Demons said:

The idea I have in mind is that it's going to be huge, I mean massive as it is meant to test patience and sense of direction.

Just be aware of the fine line between patience and frustration.

So I am going to take a lot of this advice to heart. I will say that elevation variation is something to consider and might add to the overall feel of what I am going for. Ideally, what this is supposed to be is supplementary to a creepypasta (which is inspired by a much larger creepy pasta) that I am writing, well, not quite. So I am going to write that up first to give me the basic inspiration and then create the level around the story. Once I have something I will update this page (of course). 

@Kappes Buur Following my post I did do some supplementary research to avoid frustration. I saw some indie games based on the "Back Rooms" /x post and yeah, they seem to have some variety in terms of office supplies, different rooms. So I can still fundamentally stick with the basic idea and then branch off for some creative liberties. Ideally, I do know i want people to find an exit. This is probably an idea that is going to take a long long time to make given that generating interest over long projects like this can be a chore. I take a look at beasts like Hurt and Verdant Citadel as well as some Sunder Maps and notice that there is always something to keep the attention of the audience so that is something to consider. Originally, I was thinking of making it a larger version of Hunted from plutonia where I would have a group of archviles wake up upon maze enterance and your goal would be to make it to the exit without being hunted by the "beings you can hear but not see". Their laugh hunting sound is perfect ambience. But I might through a few zombies and imps to break some of the tension. Ideally, I am trying to create a clostrophobic and unsettling atmosphere in a office decay settiing. But being that the protag is supposed to be a SCP MTF member, maybe I could go a little more action oriented in practice. 

@Misty, what map editor would you suggest, I also have Doom Builder 2. I would like the wad ideally compatible with weapons mods and what not so I don't want to make a mistake of having the level only compatible with a certain source port (hence why I am not going for Realm monsters or custom textures). 

To get a better idea of what I am doing here are my inspirations: 
http://www.scp-wiki.net/
https://www.creepypasta.com/the-backrooms/
http://www.scp-wiki.net/task-forces