Honestly, I just used LibreOffice Writer and a thoroughly-annoying amount of formatting, along with some free fonts (Chomsky for the title, Old Newspaper Types for everything else).
I wish it were more elaborate, but it was very low-tech, and I made it the night before the session!
The template link is at the bottom of my original post. Or were you asking for my specific copy? If so I'll see if I can put it somewhere for download
I switched from Roll20 to foundryvtt due to lack of updates and performance from roll20. While there is no marketplace to purchase official adventures, I have the dmsguild avernus pack that includes all the maps, so uploading the map and drawing walls/dropping tokens doesnt take me too long. The maps from dmsguild are vastly higher quality than the roll20 avernus maps that are bundled.
Havent used fantasy grounds in a long time, but the interface was bad enough to turn me away from using it. The questions should really be: what VTT do you want to invest in?
Roll20 may be free, but all the decent features require a subscription, and even then you have to do all the work finding and adding scripts and writing macros.
Fantasy grounds has the higher upfront cost ($100?), but like you see - the modules are cheaper, but you have to host it yourself and the interface is kinda poop.
FoundryVTT is a newcomer, but has only an upfront cost of $50- and then you can choose how you want to host it - locally or on a cloud server. It does however lack anything past the SRD, but community modules are being developed like ones that can import your dndbeyond content, so potentially foundry+dndbeyond could contain all your sourcebooks/adventures. Not exactly a downside as well, but it probably suits those who are more technically inclined, especially if you want to customize it heavily.
For now the best way is to use Posterazor found here: http://posterazor.sourceforge.net/
Just set the "Absolute size" in step 4 to whatever the x by y in squares are.
Right now I am trying to figure out how I will release them in the future so please excuse this extra work!
It's ok, I had to fix it lol. I just looked up on google "hell" or "hellscape" with 1920x1080 dimmensions and found a few different styles for different parts (i.e on avernus floor etc) Otherwise I just used Canva.com to make everything from stratch
There is one of the war machines available on Amazon. Maybe you can do some random encounters with them. I believe there is some lore in the back of the book. And there is some fun stuff on the DM screen available for Avernus. https://www.amazon.com/WizKids-Icons-Realms-Baldurs-Infernal/dp/B07RH2T2BH