I've made hundreds of worlds in Minecraft since 1.7, less so since 1.13 due to the slower make time (thanks, Mojang!), and yet despite spawning in or near any biome I can think of, even uber-rare ones like mesa bryces, iceberg plains, redwood hills, even mushroom island shores, I have never spawned exactly in a roofed forest. Always in a plains biome next to it or some type of forest.
Anyone else experiencing this, or am I going nuts?
Hmm... I spawn in them fairly often (1.10 to 1.12.2 more so all the time besides Plains), only once in 1.14 I spawned near a Ice Spikes biome which I hadn't in years, and during a 1.12.2 world spawn during a video I was doing I got a Mesa Biome. But just recently I got a Roofed Forest Biome in 1.13 for something else in maybe a recent change from the mostly Plains biomes. I get the common biomes mostly more than the rare ones. Plains, Roofed Forest (usually neighbouring a Plains of course), Beaches (hate when I see sand and its not a Desert).
For me the last time I got Ice Spikes compared to my 1.14 instance was I think 1.7.10 a long while a go. Other than that from not specifying world seeds all the time that I leave it blank in the box. I get common 90% of the time I think/feel and otherwise its a 0.5% chance I get the other biomes, maybe even less. But that's just speculation as I don't always keep track of the biomes I spawn in due to commonly seeing Plains or Roofed Forests. But I never find a Roofed Forest with the Woodland Mansion obviously so it isn't great sometimes if I wanted a reason to have a Roofed Forest besides the Mushrooms.
The 1.13.2 seed I got recently that I remember is this:
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This is from 1.6.4 but Mojang has never updated the biomes to account for additional biomes in later versions (including variants other than the ones listed). Since roofed forests have plains as a sub-biome this means that you'll nearly always spawn within them instead; I say "nearly" because the game searches a +/-256 block square around the origin for a valid biome and if none is found it begins a random walk which can travel well over 1000 blocks away from 0,0 before it finally gives up and spawns you at whatever the last point was. Usually though, it will stop when it finds a grass block with a direct view of the sky, which possibly could be in a roofed forest.
Here is a more extreme example from the seed "-1984348358409562691" in 1.6.4, which ended up more than 1500 blocks away from the origin due to no land (excluding mushroom islands, which are not valid since they do not have grass. The bits of exposed ocean are valid but it never landed on one):
One other possible way you could spawn in a roofed forest is if the initially chosen point is a valid biome but it is underwater or otherwise is not an exposed grass block (note that this only applies to the exact world spawn point; the actual player spawn point is randomly located nearby and may be on any block). in which case the game will do a random walk but it will typically not go very far, and it just might land in a roofed forest (the presence of trees may block the view but since chunks are not populated unless a 2x2 chunk area has been generated, with the center being populated, they usually won't present when the check is done).
Yeah, it can feel like this, but after Roughly 400'ish, I must've originally-spawned in a Roofed ( /now-Dark) Forest at least 3X (though as the other poster wrote above it's yes, of-course Mostly Plains [with generally the rarer-Biome even in the distance, not-right next, to one]). I was interested in this topic because, they are an alternative to Jungle (which Lags-worse generally for most, than anything except perhaps the more-Blocks of Hillier, often more-technical Biomes), for a "Hack your way out" theme.
Not to spoil the fun, but I find that Like Jungle there are relatively-obvious ways to even find pseudo-"clearings" (though there technically Are-none, in any mainly-Treed, Biome) of safe-enough size, simpler than just trying to make a "Clear-Cut" (which takes Hours) to avoid Hostiles. At which point I went back to Planting Trees outside Base, to keep Tree Farming interesting.
But I recommend the Burning ones. "Heh" (also Burns better-than Jungle, just saying >.> not just more interestingly <.< ).
My solution to Slow-Generation times, is to activate my Force Quit option and walk-away, for at least a little while. It auto-Pauses the Game and keeps-Generating, of course (faster), on that.