diff --git a/build.sh b/build.sh
new file mode 100755
index 0000000..4bf5418
--- /dev/null
+++ b/build.sh
@@ -0,0 +1,78 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Build BusyBox with ARM toolchain from env.sh and optional sysroot.
+#
+# Usage:
+#   ./build.sh [SYSROOT]
+#
+# Examples:
+#   ./build.sh
+#   ./build.sh /home/stargazer/arm-uclinuxfdpiceabi/sysroot
+
+TOOLCHAIN_PREFIX="${TOOLCHAIN_PREFIX:-arm-uclinuxfdpiceabi}"
+CC_BIN="${CC_BIN:-${TOOLCHAIN_PREFIX}-gcc}"
+STRIP_BIN="${STRIP_BIN:-${TOOLCHAIN_PREFIX}-strip}"
+JOBS="${JOBS:-$(nproc)}"
+INSTALL_DIR_NAME="${INSTALL_DIR_NAME:-_install}"
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+BUSYBOX_DIR="${SCRIPT_DIR}/busybox"
+SYSROOT_DEFAULT="/home/stargazer/arm-uclinuxfdpiceabi/sysroot"
+SYSROOT="${1:-${SYSROOT:-$SYSROOT_DEFAULT}}"
+ENV_FILE="${ENV_FILE:-${SCRIPT_DIR}/env.sh}"
+
+die() {
+  echo "ERROR: $*" >&2
+  exit 1
+}
+
+if [ -f "${ENV_FILE}" ]; then
+  # shellcheck disable=SC1090
+  . "${ENV_FILE}"
+fi
+
+if ! command -v "${CC_BIN}" >/dev/null 2>&1; then
+  die "Compiler not found in PATH: ${CC_BIN}"
+fi
+if ! command -v "${STRIP_BIN}" >/dev/null 2>&1; then
+  die "Strip tool not found in PATH: ${STRIP_BIN}"
+fi
+if [ ! -d "${BUSYBOX_DIR}" ]; then
+  die "busybox directory not found: ${BUSYBOX_DIR}"
+fi
+if [ ! -d "${SYSROOT}" ]; then
+  die "SYSROOT not found: ${SYSROOT}"
+fi
+
+INSTALL_DIR="${SCRIPT_DIR}/${INSTALL_DIR_NAME}"
+if [ "${INSTALL_DIR}" = "/" ]; then
+  die "Refusing to install into /"
+fi
+
+echo "Compiler: ${CC_BIN}"
+echo "Strip: ${STRIP_BIN}"
+echo "SYSROOT: ${SYSROOT}"
+echo "Source dir: ${BUSYBOX_DIR}"
+echo "Install dir: ${INSTALL_DIR}"
+
+cd "${BUSYBOX_DIR}"
+
+if [ ! -f ".config" ]; then
+  make defconfig
+fi
+
+make oldconfig
+make -j"${JOBS}" \
+  CROSS_COMPILE="${TOOLCHAIN_PREFIX}-" \
+  CC="${CC_BIN}" \
+  STRIP="${STRIP_BIN}" \
+  EXTRA_CFLAGS="--sysroot=${SYSROOT}" \
+  EXTRA_LDFLAGS="--sysroot=${SYSROOT}"
+
+make CONFIG_PREFIX="${INSTALL_DIR}" install
+"${STRIP_BIN}" busybox
+
+echo "Build completed successfully."
+echo "Binary: ${BUSYBOX_DIR}/busybox"
+echo "Installed to: ${INSTALL_DIR}"