Hi wielkiczarnyafgan,
Eric and I are in the process of doing exactly this. We’ve got a good start with basic lighting troubleshooting and tips on our Wiki Lighting guide (Located in my signature). We have plans to add a lightmass troubleshooting section along with some more UV lightmap oriented sections.
You can follow progress in my post here: https://forums.unrealengine/showthread.php?56777-Photons-Be-Free-Mini-tutorials-and-other-curiosities&p=220501&viewfull=1#post220501
I’ve got the ones listed that are done, ones that are being worked on, and ones that are eventually planned to get up. Unfortunately, neither Eric nor myself have had the time lately to get these completely finished.
Lightmass is definitely one that is asked about very often.
In the mean time, if you’ve not already seen our documentation with lightmass you can check that out here. It’s not a how-to, but it’s got a lot of information that is helpful.
https://docs.unrealengine/latest/INT/Engine/Rendering/LightingAndShadows/Lightmass/Basics/index.html
https://docs.unrealengine/latest/INT/Engine/Rendering/LightingAndShadows/Lightmass/index.html
https://docs.unrealengine/latest/INT/Engine/Content/Types/StaticMeshes/LightmapUnwrapping/index.html
https://udn.epicgames/Three/Swarm.html
There are plans for a lighting video series as well to go over some of the basics as well. No eta yet for when that will be posted, but keep an eye on the learn tab in the launcher! 
Just to go over some of the other things that you mention:
Long build times: There are a few factors that can cause this. Hardware specs, number of meshes or complications of your scene, number of lights, Lightmap resolutions, calculations of bounce, whether there is a lightmass importance volume in your scene, size of world, and some other contributing factors depending on if settings have been adjusted in the world settings for lightmass.
All of these can affect your light build which makes it very difficult to give a general answer for why light builds take a while. 
I’m working on getting something helpful together though. These questions do come up quite often.