Hopefully this works.

Build.php

@@ -0,0 +1,235 @@
+<?php
+
+declare(strict_types=1);
+
+$RootDirectory = __DIR__;
+$OutputDirectory = $RootDirectory . "/_Site";
+$PagesDirectory = $RootDirectory . "/Pages";
+
+
+function RemoveDirectory(string $Directory): void
+{
+    if (!is_dir($Directory)) {
+        return;
+    }
+
+    $Iterator = new RecursiveIteratorIterator(
+        new RecursiveDirectoryIterator(
+            $Directory,
+            FilesystemIterator::SKIP_DOTS
+        ),
+        RecursiveIteratorIterator::CHILD_FIRST
+    );
+
+    foreach ($Iterator as $Item) {
+        if ($Item->isDir()) {
+            rmdir($Item->getPathname());
+        } else {
+            unlink($Item->getPathname());
+        }
+    }
+
+    rmdir($Directory);
+}
+
+
+function CopyDirectory(
+    string $Source,
+    string $Destination
+): void {
+    if (!is_dir($Destination)) {
+        mkdir($Destination, 0777, true);
+    }
+
+    $Iterator = new RecursiveIteratorIterator(
+        new RecursiveDirectoryIterator(
+            $Source,
+            FilesystemIterator::SKIP_DOTS
+        ),
+        RecursiveIteratorIterator::SELF_FIRST
+    );
+
+    foreach ($Iterator as $Item) {
+        $RelativePath = $Iterator->getSubPathName();
+        $DestinationPath = $Destination . "/" . $RelativePath;
+
+        if ($Item->isDir()) {
+            if (!is_dir($DestinationPath)) {
+                mkdir($DestinationPath, 0777, true);
+            }
+
+            continue;
+        }
+
+        copy(
+            $Item->getPathname(),
+            $DestinationPath
+        );
+    }
+}
+
+
+function RenderPage(
+    string $SourceFile,
+    string $DestinationFile,
+    string $RootPath
+): void {
+    $DestinationDirectory = dirname($DestinationFile);
+
+    if (!is_dir($DestinationDirectory)) {
+        mkdir($DestinationDirectory, 0777, true);
+    }
+
+    ob_start();
+
+    try {
+        require $SourceFile;
+        $Contents = ob_get_clean();
+    } catch (Throwable $Exception) {
+        ob_end_clean();
+
+        throw $Exception;
+    }
+
+    if ($Contents === false) {
+        throw new RuntimeException(
+            "Failed to render: " . $SourceFile
+        );
+    }
+
+    file_put_contents(
+        $DestinationFile,
+        $Contents
+    );
+}
+
+
+/*
+ * Remove the previous build.
+ */
+
+RemoveDirectory($OutputDirectory);
+
+mkdir(
+    $OutputDirectory,
+    0777,
+    true
+);
+
+
+/*
+ * Copy static directories.
+ */
+
+$StaticDirectories = [
+    "Assets",
+    "Scripts",
+    "Styles"
+];
+
+foreach ($StaticDirectories as $Directory) {
+    CopyDirectory(
+        $RootDirectory . "/" . $Directory,
+        $OutputDirectory . "/" . $Directory
+    );
+}
+
+
+/*
+ * Copy index.html.
+ */
+
+copy(
+    $RootDirectory . "/index.html",
+    $OutputDirectory . "/index.html"
+);
+
+
+/*
+ * Build PHP pages.
+ */
+
+$Iterator = new RecursiveIteratorIterator(
+    new RecursiveDirectoryIterator(
+        $PagesDirectory,
+        FilesystemIterator::SKIP_DOTS
+    )
+);
+
+foreach ($Iterator as $File) {
+    if (!$File->isFile()) {
+        continue;
+    }
+
+    if (strtolower($File->getExtension()) !== "php") {
+        continue;
+    }
+
+    $SourceFile = $File->getPathname();
+
+    $RelativePath = substr(
+        $SourceFile,
+        strlen($PagesDirectory) + 1
+    );
+
+    $RelativePath = str_replace(
+        DIRECTORY_SEPARATOR,
+        "/",
+        $RelativePath
+    );
+
+    /*
+     * Anything under Pages/Bits is a partial.
+     * Do not generate HTML pages from these.
+     */
+
+    if (str_starts_with($RelativePath, "Bits/")) {
+        continue;
+    }
+
+    $OutputPath = preg_replace(
+        "/\.php$/i",
+        ".html",
+        $RelativePath
+    );
+
+    if ($OutputPath === null) {
+        throw new RuntimeException(
+            "Failed to create output path for: " . $SourceFile
+        );
+    }
+
+    /*
+     * Pages/Home.html
+     *     RootPath = ../
+     *
+     * Pages/Stuff/Page.html
+     *     RootPath = ../../
+     */
+
+    $Depth = substr_count(
+        $OutputPath,
+        "/"
+    ) + 1;
+
+    $RootPath = str_repeat(
+        "../",
+        $Depth
+    );
+
+    $DestinationFile =
+        $OutputDirectory .
+        "/Pages/" .
+        $OutputPath;
+
+    echo "Building Pages/" . $OutputPath . PHP_EOL;
+
+    RenderPage(
+        $SourceFile,
+        $DestinationFile,
+        $RootPath
+    );
+}
+
+
+echo "Build complete." . PHP_EOL;