I want to create a building/ structure in unity for my game. Would it be better to model the building in a modelling package such as blender or use a series of cubes for walls built in unity?
Note: I have no modelling expirence
Use Blender. The primitives in Unity are only for simple prototyping.
–Eric
Use Ürban PAD! If you’re modeling buildings, it’s easy to get started, create simple geometry, add variety and LOD to a single building, and regenerate to get a different look.
Here are links to a few basic tutorials on how to make a building at both simple and intermediate levels of detail:
Watching the Urban PAD Youtube videos now, looks like a very cool program. I like the procedural approach that actually shows the flow graph. The question is can you step back and branch out options in those flow graph? (like SideFX Houdini’s Channels and SOP)
Also, a suggestion, I think its great you guys have a Youtube channel, showing features through video is million times better than just words and images. But your videos are silent - (maybe its just me) I would like to hear some commentary plus it adds that “closeness” to your potential customers so that we know your software isn’t coded by some robot, but a human on the other end!
Let me tell you what you should do! Do a script that makes buildings proceduraly!!
Thanks, Bawss. We agree with you on the videos, but our one-man video department takes a little longer to crank out sound. We’ll take this into consideration for the next ones, though! No robots here 
Concerning branch creation in the node graph, we don’t currently have this function. What we do have is something that approximates branch creation: linking templates to each other with the Sector Link function (in the Decoration menu of the Sector Editor component). This way you can link a variable roof to a variable building base, for example. This keeps the final model easier to manage in the graph.
You can see how sector linking works in the following video, which features in-place template editing in the current version:
Depends what kind of building you want. If its just scenery then do it in an external program. But if you want the player to interact with it then create it in unity.