diff --git a/.github/BUILDING.md b/.github/BUILDING.md
index 9f5a13360..f3a6e6244 100644
--- a/.github/BUILDING.md
+++ b/.github/BUILDING.md
@@ -3,9 +3,13 @@
 
 ### The dependencies for Debian-like distributions.
 ```   
-sudo apt install build-essential cmake libunwind-dev libsox-dev git libasound2-dev nasm g++-14
+sudo apt install build-essential cmake pkg-config libunwind-dev libsox-dev git libasound2-dev nasm g++-14 \
+  libudev-dev libxcb1-dev libx11-dev libwayland-dev libxkbcommon-dev libxrandr-dev \
+  libxinerama-dev libxcursor-dev libxi-dev libxext-dev
 ```
 
+Without `pkg-config` and `libudev-dev` the configure step fails (Vulkan-Loader and hidapi respectively); without the X11/Wayland headers Vulkan-Loader and GLFW are built without window-system support. This list matches what CI installs (`.github/workflows/rpcsx.yml`).
+
 ### The dependencies for Fedora distributions:
 
 ```
@@ -34,3 +38,12 @@ For Ubuntu 24.04 you need to manually specify compiler version:
 ```
 cmake -B build -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_FLAGS_INIT="-march=native" -DCMAKE_CXX_COMPILER=g++-14 && cmake --build build -j$(nproc)
 ```
+
+### Building with clang
+
+clang 20 or newer is required: clang 18 rejects the codebase's C++23 relaxed `constexpr` (P2448, e.g. in `rx/StaticString.hpp` and `rpcsx/gpu/lib/gcn-shader/src/eval.cpp`), and clang 19 fails on the enum-reflection code in `rx/format.hpp` (its `-Wenum-constexpr-conversion` diagnostic is not SFINAE-friendly). The matching `clang-tools` package is also needed, since CMake invokes `clang-scan-deps` for dependency scanning:
+
+```
+sudo apt install clang-20 clang-tools-20
+cmake -B build -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_FLAGS_INIT="-march=native" -DCMAKE_C_COMPILER=clang-20 -DCMAKE_CXX_COMPILER=clang++-20 && cmake --build build -j$(nproc)
+```