I've worked on a tower in Minecraft.
Here are the Instructables.

Step 1: Things You Need

Things you need :
Minecraft Beta 1.5
36 Wood
153 Wooden planks
9 Glass
17 Wooden half slaps
16 Wooden stairs
24 Fances
8 Ladders
8 Trapdoors
22 Torches

Step 2: The Base

Pic 1 Place blocks
Pic 2 Stack up
Pic 3 Complete

Step 3: The Walls

Pic 1 Build wherever you want
Pic 2 Build wherever you want
Pic 3 Complete first walls
Pic 4 Build a floor
Pic 5 Leave a hole
Pic 6 READ NOTES
Pic 7 Build walls
Pic 8 READ NOTES
Pic 9 READ NOTES
Pic 10 Complete walls
Pic 11 Build floor
Pic 12 Leave a hole above your other one

Step 4: How to Stack Up Fences

Pic 1 Place 2 blocks
Pic 2 Place fence on it
Pic 3 Remove the block under the fence
Pic 4 Pace Fence

Step 5: Building the Roof

Pic 1 Place fences like this
Pic 2 Build
Pic 3 Stack up walls
Pic 4 build
Pic 5 Place half slaps
Pic 6 Place stairs between them
Pic 7 Build
Pic 8 Place half slabs in front of the stairs
Pic 9 Build
Pic 10 Place wooden planks
Pic 11 Place stairs
Pic 12 Place half slabs
Pic 13 Place Glass

Step 6: Complete the Tower

Pic 1 Remove sand/grass/stone and place wooden planks
Pic 2 Complete the floor
Pic 3 Build stairs
Pic 4 Build stairs
Pic 5 Tower for now
Pic 6 Place trapdoors
Pic 7 Another look
Pic 8 Place all trapdoors under and above windows as shown
Pic 9 In beta 1.7 place torches on fences
Pic 10 In beta 1.6 or lower place on floor
Pic 11 Complete it
Pic 12 Place torches on walls
Pic 13 Finish your tower