For information about building an implementation guide (both in terms of structure and tooling) see documentation here: https://confluence.hl7.org/display/FHIR/IG+Publisher+Documentation
The built/online version of this guide can be seen here: http://build.fhir.org/ig/IHTSDO/snomed-ig/
This IG uses FSH.
To install (tested with version 0.14.0):
npm install -g fsh-sushi
To build using HL7 IG Publisher and Ontoserver:
cd snomed-ig
java -Xmx4G -jar publisher.jar -ig . -tx https://r4.ontoserver.csiro.au/fhir