I've never had any wooden builds (village buildings, since I don't "build") burn down due to lightning, including a village right in the spawn chunks, with more than 2,500 hours of time in the world (lighting does appear to strike in spawn chunks as long as they are loaded since people have made charged creeper farms that rely on this. If I were playing in 1.8+ I'd be more concerned about the villagers being turned into witches), which can really only set structures on fire in exceptional circumstances, such as striking just as it stops raining so the fire isn't put out, or just next to an overhang that is low enough for the fire to spread to it (lightning only strikes blocks with a direct view of the sky but can start fires within a 3x3x3 area around it). In fact, I only recently saw any clear evidence of lightning damage in more than 4 years of playing, after a thunderstorm in a mod biome, which likely occurred due to the high flammability of leaves (they are more likely to catch fire and spread it than wood) and the numerous overhangs due to the irregular canopies.
The first 7000 or days or so of my current world were spent first in a Desert biome, then Mesa, then Ice Spikes - all of which have no precipitation. This was probably the main reason why I never saw a charged creeper - after a fourth move to a roofed forest area bordering a swamp biome, I saw my first charged creeper not long after, followed by a few others. I also saw a pig turn into a pigman after a strike nearby.
In terms of fire damage from lighting strikes, I always assumed the rain would put any fire out. The only problem would be therefore if straight after a strike the storm cleared, so whatever was burning could carry on burning. I assumed this was what happened when I came outside after storm once in my roofed forest base to find a large mega spruce tree I planted (several times too to get the shape I wanted) was nothing more than a few blocks and leaves. I have built a wooden house in my current area, but I gave it a stone roof, and made sure the roof extends past the house by one block each side. However I don't know if a lightning strike close by can set the wood alight or if it strikes the roof whether a flammable block beneath could catch light. Its still ok tho as I speak
So you need an overhang of at least 2 blocks - and actually, more since fire itself can spread to blocks within a 3x3 -1 +4 area around itself (+/- 1 block away from lightning + 1 blocks away from fire block in all directions except for up, which is 4 blocks):
for (int k = -1; k <= 1; ++k)
for (int l = -1; l <= 1; ++l)
for (int i1 = -1; i1 <= 4; ++i1)
(add one more block in each direction to account for lightning starting fires up to 1 block away)
Also, lightning can damage/affect entities up to 3 blocks away (9 above) from where it strikes, another thing that needs to be taken into consideration - so the overhang and ceiling need to be at least 4 blocks, possibly 6 high (5 inside + 1 roof) if the "bottom edge" includes any part of an entity (villagers are 1.95 blocks high):
When lightning strikes, all entities within a 6×6×12 region horizontally centered on the northwest corner of the target block with the bottom edge 3 below the target block are struck by lightning.
(whether any of the villagers that I have have ever been struck is unknown since I play in 1.6.4, so they can only get damaged, and 4 strikes are needed to kill them; it is very unlikely that the villagers I trade with will get struck that many times between rounds of trading, which heal them. Also, this gives you some idea of the size of my world, with a total of 11 villages, none of which (the ones in plains) have ever had any lightning-related damage. Not saying that it doesn't happen but it seems to be very unlikely to happen; I've also had many other worlds with perhaps a couple dozen villages altogether)