Right, think I’ve cracked it. For anyone else who encounters issues with this and are approaching from a bit of a noob angle like I did, here is my workflow process from finishing building the mesh through to putting it into the engine which may be of help to someone (many thanks to the dozens or articles, threads and especially wonderful tutorial on building a second lightmap channel in Blender which essentially I’ve used to do the second half of my workflow). You may note I begin my build in Sketchup. I can use Blender (which would skip some steps for exporting -> importing to Blender), but for basic architecture construction, I find Sketchup’s construction system very easy and quick to handle:
Workflow Process:
Create item in Sketchup
Export item as a Collada file (only file type possible on basic Sketchup, Pro version has more file options)
Open blender
Delete start up items if they still appear in your work space
Import mesh (remember to select import from Collada file as that is what Sketchup exports as)
As soon as it’s imported, hit Ctrl+J to merge all meshes into one single mesh
Select either Flat or Smooth Shading from right hand menu in Blender to suit
Scale x100 (this will perfectly align the scale used in Sketchup with UE4’s scale)
Switch to Edit Mode
Go to Menu -> Select all Vertices
Go to Mesh -> UV Mapping -> Unwrap
Select whole item in upper left menu
Select the Mesh button on the left hand tabs
Click the “+” sign next to UV maps
Keep new UV map selected and switch to UV Editor
Press the “+” sign next to New
Call it Lightmap and click okay (making sure it is at 1024x1024).
Go back to 3D View, switch to edit mode and select whole model
Press space and seek out and select Smart UV Project. Press Okay.
Switch back to UV Editor and select the lightmap channel.
Make sure it is all selected and then hit Ctrl+A and then Ctrl+P
Switch back to 3D View and adjust the margin to 0.1
Export model to FBX
Import model into Unreal 4
Open up the Static Mesh Editor for the model
Add material
Adjust Lightmap Resolution to 1024 (for me, lower than this just doesn’t seem right)
Place object into the level. Rebuild Lights. (Don’t forget to have a lightmass volume).
And viola, I now have some correctly shaded architecture as can be seen with the arch and door frame in this picture (ignore the other meshes at the moment, I still need to apply this process to them):
So where was I going wrong? Multiple places I think. Firstly, there was an issue with the Sketch Up -> Blender import. Somewhere in that process, the mesh gets broken down from a single Sketchup mesh into multiple meshes in Blender. Doing the Ctrl+J after import fixes that issue, merging it all back as a single mesh. Of course, as the mesh is in multiple parts, this was playing havoc with trying to generate UV maps (which was a part I was originally struggling with last night), however once the multiple mesh issue was fixed, it’s just a case of first building a UV map and then pretty much following 's YouTube tutorial for building a second UV map and everything else slots into place. Oh, and using FBX was an export file from Blender also helps. I did originally try with OBJ (as that was the format years ago I used to export between Gmax and Bryce), but FBX also seems to have better results, correct orientation and is pretty much what everyone else uses.
Good job I’ve got the day off today due to industrial action in work, because now I’ve got to go through and do this to the 30+ meshes I’ve all ready built and replace them in my work in progress!