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).
As Drmixable mentioned, it is very situational. If you're intending to solely be a kill lane, it might make sense to go Sapphire Crystal, ward, health pot, then tears.If you do this, you are gambling completely on your lane getting first blood and then compounding that advantage into laning dominance for the rest of the laning phase.
If you are wanting to be a more traditional support early game, then definitely do the standard Faerie Charm, wards, health pots mix.
Even if you do start with the mana crystal and go straight into tears, I think it still makes sense to move towards the more traditional support build after you pick up the tears. Philo stone, Heart of Gold, lots and lots of wards, oracles, etc. Build your gp10 items into their upgrades, prioritizing Shurelya's if your team is winning team fights and Locket if they are not.
And - as always - buy boots on your second trip back to base. For Blitzcrank, Boots of Mobility upgrade later makes a lot of sense for getting into position to yoink someone or knock them up to protect your carry. However, if the team is full of hard CC you will of course want the tenacity from merc treads instead.
Other good items include getting an early catalyst(which will build into Banshee's later), to sustain your lane harass and increase your passive shield proc if necessary. An aegis, of course, is always welcome from a support. Frozen Heart could be viable if the enemy team has more than two sources of straight auto attack damage, but generally won't be worth it.
Hopefully this wall of text gets you started on the path to thinking about how to apply your items to each situation. There is no single item guide that any hero should follow. Anything from who you are facing, how much gold you have, and how late it is in the game can vary your items and the order you build them in.
GL HF!
Best Answer
The 'Blue Ezreal' build focuses around poke items, compared to the typical ADC build which would focus more on autoattack damage and less around poking with Q. Both builds are high damage, but differ on the situation.
If your team is designed around fast engages, the Blue Ezreal isn't as good as the typical ADC Ezreal: As stated before, Blue Ezreal shines when poking and/or chasing (due to the slow of gauntlet)
Many people get Elder Lizard prior to Tears due to it's decent damage and on-hit feature. Although getting Tears first to start stacking it early may seem like a good idea, it sometimes can cause you to become too behind in lane (depending on matchup) since it provides no damage or health/sustain, and therefore a lot of players opt to rush the Elder Lizard first, since it provides an easier laning phase, supplying you with HP regen and damage, for better damage trading with the opponent. It also builds from 2 longswords, so you can grab them earlier to bully your opponenets.
That being said, it is possible to get Tears first to start stacking it early, but, you might find yourself struggling in lane more, depending on matchup.