Bukkit

Many have faced the problem of copying buildings with WE. This could be your solution!
This plugin will find all blocks of a building. All you have to do is specify at which blocks you want to stop searching.

How to use?

Simple! Just take a bedrock block (or the one you have configured!) and enter delimiting block types with
/bd <item IDs seperated by commas>
Then click on a block of your building.
The plugin will automatically search all Blocks connected with the clicked one.
Then type /bd select to convert it into a WorldEdit selection.
Done!
(Unless you are OP you will need the "buildingdetector" permission node)

Any side effects?

Well if you don't specify all block types which surround the object you want to select you will lag the hell out of your server until the maximum number of blocks is reached. Then the process stops and tells you it has failed!
Another side effect is that /bd select will create a cuboid selection... The two outermost points of your selection were taken..

Dependencies

WorldEdit obviously.

Configuration

There are two entries in the configurations file.
item: 7
maxBlocks: 100000
If you don't want to be bedrock the item (i.e. you have LogBlock or anything where you want Bedrock to be the linked item) change the item property.
If you want to select objects larger than 100000 blocks then you have to alter the maxBlocks property.