0)Unity 3d should be used, c# for scripting.
1)The user should able to set 3d cubes in a flat ground and over/side other cubes
2)Physics should be used to cubes. (all cubes weights the same) and collision among them.
3)Cubes are generated by clicking an image of a cube in a simple gui (gui symbol got selected)
4)User click in a part of the screen and a cube is appears in that part (picking should be used to determine 3d site where the cube should "emerge" in that position), please the picking system should be clear for the user showing a clear blue circle sing of where the mouse is picking in the 3d scene. (could be another cube or the land, no other possibility)
5)Gravity should be enable, with "similar" value to 9,8 m/s^2
6)User can select a texture from a set of predefined loaded textures (visible in a preview box in the gui, just like cube symbol) and after clicking on a cube (picking should be used again), the texture is apply over the whole cube selected. Use low resolution textures. Max 512x512.
7)Camera should be easy to control to allow to pan around, use mouse wheel for zoom in zoom out into the frustum direction., use mouse move after selecting a "icon camera" to rotate around by "click and move" (it is an standard inverse drag map algorithm that you can get in the web ;-) ). You are free to suggest any other algorithm that you find more suitable
8)Green repeated texture should be used for flat land.
9)An skydome should be used for the whole environment, suggested theme: a simple illuminated cloudy sky.
10)A delete symbol in the gui that after selected and clicking in a CUBE (picking again), should remove that cube from scene.
11)Please make sure that after setting a cube along another the initial position does not generate a strong collision but is positioned without a problem one next each other.
To make sure that you have created the physics for cubes correctly, removing base cubes of a tower should allow the dropping of the above structure. Please make that test.
12)Create a canvas in facebook, with the proper page configuration to play the game there, Hosting in our side.
13) Just that.