diff --git a/block.go b/block.go
new file mode 100644
index 0000000..c1a323e
--- /dev/null
+++ b/block.go
@@ -0,0 +1,20 @@
+package merkle
+
+const (
+	// MaxBlockSize reasonable max byte size for blocks that are checksummed for
+	// a Node
+	MaxBlockSize = 1024 * 16
+)
+
+// DetermineBlockSize returns a reasonable block size to use, based on the
+// provided size
+func DetermineBlockSize(blockSize int) int {
+	var b = blockSize
+	for b > MaxBlockSize {
+		b /= 2
+	}
+	if b == 0 || (blockSize%b != 0) {
+		return 0
+	}
+	return b
+}
diff --git a/block_test.go b/block_test.go
new file mode 100644
index 0000000..f011828
--- /dev/null
+++ b/block_test.go
@@ -0,0 +1,17 @@
+package merkle
+
+import "testing"
+
+func TestBlockSize(t *testing.T) {
+	var testSet = [][2]int{
+		{1024 * 1024, 16384},
+		{1023 * 1023, 0}, // Not a evenly divisible
+		{1023, 1023},     // less than the max
+	}
+	for _, item := range testSet {
+		got := DetermineBlockSize(item[0])
+		if got != item[1] {
+			t.Errorf("expected %d, got %d", item[1], got)
+		}
+	}
+}
diff --git a/doc.go b/doc.go
index f9577a8..de87b64 100644
--- a/doc.go
+++ b/doc.go
@@ -4,6 +4,7 @@ What do you expect from a merkle tree API?
  - building a tree from an io.Reader
  - validating a tree from an io.Reader
 * concurrency safe
+ - any buffer or hash.Hash reuse
 */
 
 package merkle
diff --git a/node.go b/node.go
index 943139b..b46007c 100644
--- a/node.go
+++ b/node.go
@@ -2,25 +2,45 @@ package merkle
 
 import (
 	"crypto"
-	_ "crypto/sha1"
+	_ "crypto/sha1" // to satisfy our DefaultHash
 	"fmt"
+	"hash"
 )
 
 var (
+	// DefaultHash is for checksum of blocks and nodes
 	DefaultHash = crypto.SHA1
 )
 
+// HashMaker produces a new has for use in making checksums
+type HashMaker func() hash.Hash
+
+// NewNode returns a new Node with the DefaultHash for checksums
 func NewNode() *Node {
-	return &Node{hash: DefaultHash}
+	return NewNodeHash(DefaultHash.New)
+}
+
+// NewNodeHash returns a new Node using the provided crypto.Hash for checksums
+func NewNodeHash(h HashMaker) *Node {
+	return &Node{hash: h}
 }
 
 // Node is a fundamental part of the tree.
 type Node struct {
-	hash                crypto.Hash
+	hash                HashMaker
 	checksum            []byte
 	Parent, Left, Right *Node
+
+	pos int // XXX maybe keep their order when it is a direct block's hash
 }
 
+// IsLeaf indicates this node is for specific block (and has no children)
+func (n Node) IsLeaf() bool {
+	return len(n.checksum) != 0 && (n.Left == nil && n.Right == nil)
+}
+
+// Checksum returns the checksum of the block, or the checksum of this nodes
+// children (left.checksum + right.checksum)
 // If it is a leaf (no children) Node, then the Checksum is of the block of a
 // payload. Otherwise, the Checksum is of it's two children's Checksum.
 func (n Node) Checksum() ([]byte, error) {
@@ -43,7 +63,7 @@ func (n Node) Checksum() ([]byte, error) {
 			rSumChan <- childSumResponse{checksum: c, err: err}
 		}()
 
-		h := n.hash.New()
+		h := n.hash()
 
 		// First left
 		lSum := <-lSumChan
@@ -68,10 +88,13 @@ func (n Node) Checksum() ([]byte, error) {
 	return nil, ErrNoChecksumAvailable{node: &n}
 }
 
+// ErrNoChecksumAvailable is for nodes that do not have the means to provide
+// their checksum
 type ErrNoChecksumAvailable struct {
 	node *Node
 }
 
+// Error shows the message with information on the node
 func (err ErrNoChecksumAvailable) Error() string {
 	return fmt.Sprintf("no block or children available to derive checksum from: %#v", *err.node)
 }
diff --git a/node_test.go b/node_test.go
index 0ed24f1..65c6b89 100644
--- a/node_test.go
+++ b/node_test.go
@@ -6,12 +6,11 @@ import (
 	"testing"
 )
 
-var words string = `Who were expelled from the academy for crazy & publishing obscene odes on the windows of the skull`
-
 func TestNodeSums(t *testing.T) {
 	var (
 		nodes            []*Node
 		h                = DefaultHash.New()
+		words            = `Who were expelled from the academy for crazy & publishing obscene odes on the windows of the skull`
 		expectedChecksum = "819fe8fed7a46900bd0613344c5ba2be336c74db"
 	)
 	for _, word := range strings.Split(words, " ") {
@@ -20,23 +19,41 @@ func TestNodeSums(t *testing.T) {
 			t.Errorf("on word %q, encountered %s", word, err)
 		}
 		sum := h.Sum(nil)
-		nodes = append(nodes, &Node{checksum: sum})
+		nodes = append(nodes, &Node{checksum: sum, hash: DefaultHash.New})
 	}
 
+	newNodes := nodes
 	for {
-		nodes = levelUp(nodes)
-		if len(nodes) == 1 {
+		newNodes = levelUp(newNodes)
+		if len(newNodes) == 1 {
 			break
 		}
 	}
-	if len(nodes) != 1 {
-		t.Errorf("%d nodes", len(nodes))
+	if len(newNodes) != 1 {
+		t.Errorf("%d nodes", len(newNodes))
 	}
-	c, err := nodes[0].Checksum()
+	c, err := newNodes[0].Checksum()
 	if err != nil {
 		t.Error(err)
 	}
-	if gotChecksum := fmt.Sprintf("%x", c); gotChecksum != expectedChecksum {
+	gotChecksum := fmt.Sprintf("%x", c)
+	if gotChecksum != expectedChecksum {
 		t.Errorf("expected checksum %q, got %q", expectedChecksum, gotChecksum)
 	}
+
+	tree := Tree{Nodes: nodes}
+	c, err = tree.Root().Checksum()
+	if err != nil {
+		t.Error(err)
+	}
+	rootChecksum := fmt.Sprintf("%x", c)
+	if rootChecksum != gotChecksum {
+		t.Errorf("expected checksum %q, got %q", gotChecksum, rootChecksum)
+	}
+
+	expectedPieces := `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`
+	gotPieces := fmt.Sprintf("%x", tree.Pieces())
+	if gotPieces != expectedPieces {
+		t.Errorf("expected pieces %q, got %q", expectedPieces, gotPieces)
+	}
 }
diff --git a/tree.go b/tree.go
index bbd5683..fc61e2a 100644
--- a/tree.go
+++ b/tree.go
@@ -1,7 +1,41 @@
 package merkle
 
+// Tree is the information on the structure of a set of nodes
+//
+// TODO more docs here
 type Tree struct {
-	Nodes []*Node
+	Nodes       []*Node `json:"pieces"`
+	BlockLength int     `json:"piece length"`
+}
+
+// Pieces returns the concatenation of hash values of all blocks
+//
+// TODO integrate with hash size
+func (t *Tree) Pieces() []byte {
+	if len(t.Nodes) == 0 {
+		return nil
+	}
+	pieces := []byte{}
+	for _, n := range t.Nodes {
+		if n.checksum == nil || len(n.checksum) == 0 {
+			continue
+		}
+		pieces = append(pieces, n.checksum...)
+	}
+	return pieces
+}
+
+// Root generates a hash tree bash on the current nodes, and returns the root
+// of the tree
+func (t *Tree) Root() *Node {
+	newNodes := t.Nodes
+	for {
+		newNodes = levelUp(newNodes)
+		if len(newNodes) == 1 {
+			break
+		}
+	}
+	return newNodes[0]
 }
 
 func levelUp(nodes []*Node) []*Node {
@@ -13,10 +47,12 @@ func levelUp(nodes []*Node) []*Node {
 	for i := range nodes {
 		if i%2 == 0 {
 			if i == last {
-				// last nodes on uneven node counts get pushed up, to be in the next level up
+				// last nodes on uneven node counts get pushed up, to be in the next
+				// level up
 				newNodes = append(newNodes, nodes[i])
 				continue
 			}
+			//n := NewNodeHash(nodes[i].hash) // use the node's hash type
 			n := NewNode()
 			n.Left = nodes[i]
 			n.Left.Parent = n