I have made houses that can be easily placed and have an interesting limitation: they cannot be placed too close to other spawned-in houses. In other words, if you spawn in one house, you cannot place another house too close to it.

Here's a video:



Here's my commands and a explanations for a few of the harder ones:

detect the boat:
/testfor @e[type=Boat]

see if the boat is too close to something else:
/testfor @e[type=Boat,score_nearBuilding_min=1]

IF BOAT IS TOO CLOSE TO A BUILDING:

give the player a new boat:
/execute @e[type=Boat,score_nearBuilding_min=1] ~ ~ ~ /give @p boat 1 0 {display:{Name:"Shelter Blueprint",Lore:["Place a small shelter"]}}

tell the player he's too close to a building:
/execute @e[type=Boat,score_nearBuilding_min=1] ~ ~ ~ /title @p title {text:"Error",color:red,italic:true,bold:true}
/execute @e[type=Boat,score_nearBuilding_min=1] ~ ~ ~ /title @p subtitle {text:"Too close to a building!",color:red,italic:true,bold:true}

kill the boat:
/kill @e[type=Boat]

IF THE BOAT IS *NOT* TOO CLOSE TO A BUILDING:

for this part, to make the houses seem random, I used a mine cart on a circular rail. I used detector rails to power the command blocks, and powered rails to move the mine cart. When a house needed to be spawned at a boat, I would set redstone blocks next to all powered rails and quickly remove them, making the mine cart go to the next powered rail and stop until it was needed again. Here's the command I used to do that:

place redstone block(s)
/setblock <x y z next to powered rail> redstone_block

break the redstone block(s)
/setblock <x y z of redstone block> air

At this point the mine cart would move, thus triggering three commands:

clone the pre-built version of the house and the command blocks underneath w/o copying the air:
/execute @e[type=Boat] ~ ~ ~ /clone <x1 y1 z1 x2 y2 z2 of pre-built shelter> ~ ~-4 ~ masked
(The "masked" word at the end makes it so it does not copy any unwanted air- very important!)

The reason for the y placement coordinate being ~-4 is because 4 blocks under the house, I had a clock running a command, but I'll get to that in a minute.

(You can't see this in the video) play a pop sound for the nearest player:
/execute @e[type=Boat] ~ ~ ~ /playsound random.pop @p ~ ~ ~

kill the boat:
/kill @e[type=Boat]

Okay, so there's all the commands used for copying the house correctly (or not copying it, for that matter). But how did I make it so you cannot place 2 houses too close to eachother? Well, as I said earlier, I have a clock and command block 4 blocks under the house running a command (therefor the house is cloned 4 blocks under the boat, starting from the lowest point). For the clock I used a comparator clock using a redstone torch since I can lead a signal into the clock while it is at spawn, effectively turning it off. The reason it is not turned off when it is cloned is because the source of the signal turning it off is outside of the the cloned region.

Anyway, here's that command:

prevent players from spawning houses near your house:
/scoreboard players set @e[type=Boat,r=30] nearBuilding 1

That command goes along with this one I used in the beginning:
/testfor @e[type=Boat,score_nearBuilding_min=1]

And lastly, here's a picture of my setup. I hope you enjoyed and maybe learned something, and I hope my directions were not too hard to follow. Have a nice day!

picture of my setup:
http://imgur.com/bwMYlsn