Generally, each team has one jungler, which means that there will be one lane of two, and two lanes of one. Since the middle lane will always be a solo lane, this means that top and bottom will have varying numbers of champions, depending on the lane.
Top is usually considered a solo lane because the bottom lane is closer to Dragon, an important mid-game objective. Dragon is hard to solo for most non-junglers, and by keeping 2 champions in the bottom lane, it becomes quite viable to 3-man Dragon after a successful gank (or simply a double-kill). While top lane is closer to Baron Nashor, it takes quite a bit more effort to kill him - more than 3 champions in the early game can probably afford to put out. By the time Baron becomes available, the game is usually nearing the end of the laning phase, after which the difference between top and bottom lane is moot (because all 5 champions are roaming).
With a top solo lane, the champion has a leveling advantage and the potential to farm more minions (simply because there is no allied champion to compete with). Additionally, one must consider that if the other team does not have a jungler, they need to be able to successfully last 2 vs. 1. Most often, this means champions with good sustainability are better suited to the lane, such as Cho'goth, Mordekaiser, Vladimir, or Nasus.
Conversely, there are some champions who do not do well in a solo lane - these tend to be support champions like Soraka, Sona, or Janna who perform much better with a partner to buff/shield/heal. These champions usually go to the bottom lane to ensure that they are in a 2 vs. 2 situation.
In instances where there is no jungler on either team, both top and bottom will have an even number of champions. In this case you may be asked to "switch lanes" not because one lane is "better suited" than the other, but because switching lanes means changing which enemy champions you're fighting (and presumably, have been dying to).
To answer your questions:
- In your build I would take Warmog's Armor or Guardian Angel as the last item.
- I think Infinity Edge is better since it works well with Atma's Impaler
However, you cannot think like that. There is no build which is generally good. Sometimes it is better to get this item othertimes that item.
If you want a general build for Yorick I would go for this one:
- Boots of Speed + 3 or 4 health pots (4 pots - when solo top, wait near the fountain and buy 4th pot ASAP)
- Tear of the Goddess => Manamune
- probably Mercury Treads unless they have a heavy ad team, then I would go for Ninja Tabi
- straight for Atma's Impaler
- Warmog's Armor (tankier build) or Frozzen Mallet (better chasing)
- The other one of the previously mentioned items or the new item Maw of Malmortius
- Trinity Force (damage) / Guardian Angel (tanky build) / Infinity Edge (in case I have Frozen Mallet)
In case of a need I would upgrade boots before finishing Manamune, but after Tear of the Goddess. If I woudlnt be doing very well I would also get Wriggle's Lantern after Manamune or even before that and Spirit Visage, but those are items you want to sell in late game.
Early boots upgrade and Atma will give you enough resists and in combination with Manamune you will have circa 250 AD.
Finally, I think that Yorick is better with a tankier build rather than AD.
Ad NOTE: I think Nasus benefits more from a far different build. Urgot is also good with Manamune and Atma, but before Atma he really needs Brutaliser and after Atma it is better to go different items. You can also build Frozen Heart before Atma which makes you even tankier and gives you some damage, too (since you have Manamune).
Best Answer
I tested this on the PBE last night. Based on my tests, the only limiting factor in whether you can join the recall is your ping.
Contrary to what it may look like, simply walking up to the recalling player (referred to as the recaller) is not enough to join the recall. The recallee must also hit the Recall skill while in the small AoE indicator of the recaller. I assume this is to prevent accidental teleports from happening.
Because it takes some time for the recall command to travel from your own computer to the server, it might take a short while to join the recall. However, the recallee will join up as soon as the command is received. When I played yesterday, my ping was about 80, and I was able to join a recall with (approximately) half a second left before the warp happened.