tl;dr:
The checkout-deps scripts in the SourceMod repository will download the appropriate dependencies into the layout it expects; you then need to pass the correct paths to
configure.py.
The process of building an extension is effectively the same as
building SourceMod itself; you need to clone
the SDK repository and checkout each branch into its own folder (if you're doing TF2, you just need to checkout
tf2 into
hl2sdk-tf2), then pass
--hl2sdk-root with the directory containing the parent of all of those folders.
The standard directory layout is below:
/path/to/alliedmodders
├─ hl2sdk-blade
├─ hl2sdk-bms
├─ [... more hl2sdk branches omitted for brevity]
├─ hl2sdk-proxy-repo
├─ hl2sdk-sdk2013
├─ hl2sdk-tf2
├─ mmsource
└─ sourcemod
So once you've downloaded the code dependencies you'd likely want to pass the following to
configure.py (using the VS x86 tools command prompt):
--hl2sdk-root /path/to/alliedmodders --mms-path /path/to/alliedmodders/mmsource --sm-path /path/to/alliedmodders/sourcemod --sdks tf2
You may also want to run
configure.py --help to list available options, as they may be slightly different between projects.