diff --git a/Makefile b/Makefile
index aac2841..3bc6599 100644
--- a/Makefile
+++ b/Makefile
@@ -16,9 +16,10 @@ CAPNP_SOURCES=\
 	src/capnp/SegmentBuilder.java\
 	src/capnp/SegmentReader.java\
 	src/capnp/StructBuilder.java\
+	src/capnp/StructList.java\
 	src/capnp/StructPointer.java\
 	src/capnp/StructReader.java\
-	src/capnp/StructList.java\
+	src/capnp/StructSize.java\
 	src/capnp/Text.java\
 	src/capnp/WireHelpers.java\
 	src/capnp/WirePointer.java\
diff --git a/src/capnp/FromStructBuilder.java b/src/capnp/FromStructBuilder.java
index d7cf0aa..4b44e0b 100644
--- a/src/capnp/FromStructBuilder.java
+++ b/src/capnp/FromStructBuilder.java
@@ -2,4 +2,5 @@ package org.capnproto;
 
 public interface FromStructBuilder<T> {
     public abstract T fromStructBuilder(StructBuilder builder);
+    public abstract StructSize structSize();
 }
diff --git a/src/capnp/MessageBuilder.java b/src/capnp/MessageBuilder.java
index a2831e3..d54e9b8 100644
--- a/src/capnp/MessageBuilder.java
+++ b/src/capnp/MessageBuilder.java
@@ -1,5 +1,11 @@
 package org.capnproto;
 
 public final class MessageBuilder {
-    
+    public <T> T getRoot(FromStructBuilder<T> factory) {
+        throw new Error("unimplemented");
+    }
+
+    public <T> T initRoot(FromStructBuilder<T> factory) {
+        throw new Error("unimplemented");
+    }
 }
diff --git a/src/capnp/StructList.java b/src/capnp/StructList.java
index 197724a..4027907 100644
--- a/src/capnp/StructList.java
+++ b/src/capnp/StructList.java
@@ -1,10 +1,10 @@
 package org.capnproto;
 
 
-public class StructList {
-    public static class Reader<T> {
+public final class StructList {
+    public static final class Reader<T> {
         public ListReader reader;
-        public FromStructReader<T> factory;
+        public final FromStructReader<T> factory;
 
         public Reader(ListReader reader, FromStructReader<T> factory) {
             this.reader = reader;
@@ -20,4 +20,15 @@ public class StructList {
         }
     }
 
+    public static final class Builder<T> {
+        public ListBuilder builder;
+        public final FromStructBuilder<T> factory;
+
+        public Builder(ListBuilder builder, FromStructBuilder<T> factory) {
+            this.builder = builder;
+            this.factory = factory;
+        }
+
+    }
+
 }
diff --git a/src/capnp/StructSize.java b/src/capnp/StructSize.java
new file mode 100644
index 0000000..7539e0f
--- /dev/null
+++ b/src/capnp/StructSize.java
@@ -0,0 +1,13 @@
+package org.capnproto;
+
+public final class StructSize {
+    public final short data;
+    public final short pointers;
+    public final byte preferredListEncoding;
+
+    public StructSize(short data, short pointers, byte preferredListEncoding) {
+        this.data = data;
+        this.pointers = pointers;
+        this.preferredListEncoding = preferredListEncoding;
+    }
+}