The tough challenge of predicting and winning lanes.
If you never did, you really SHOULD spend atleast 1 hour actively considering startbuilds in general. In this section I will help you theorycraft around it, your ideas are as valuable as mine in the area, as long as you take the same things into account as I do.
I will divide this into a total of 4 sections. Topics listed bellow.
WARNING: This will be a long subtopic, as I consider it imperative to get a good start and having the best presets possible.
Chicken/Wards/Sentries- Who gets what and why?
Reminder: I only provide information on what is relevant when deciding on your itembuilds. It's up to you what to go with.
When soloing, you have a great number of things to take into consideration with your itembuild. "What lane am I? What am I against? What's my itempath through the game, can I skip tangos for early bottle?" Etc etc. We will go through this quite briefly, scratching the surface of things.
Remember: This is the most dangerous lane in the game! People want to kill you. First chance they get, they will attempt to do so.
What can we do to increase our chances here?
One thing I like to do is buying abnormal startitems just to increase survivability. Such as an extra circlet or an extra gauntlet at start. If I play windrunner against an aggressive lane that has great firstblood potential (Lets say Ench CM AM) then I might go for IW x2 (106) Gauntlet x2 (406) Salve/Tango (596). This gives great survivability, and not dying is vital on longlane solo. You can also drop gaunts +IW to reg full from red with salve, so it's cost-effective in that sense.
Longrangenukers such as rexxar/wr can also benefit from a single clarity, just being able to force their will by spamming spells aggressively. I find that this is not always necessary though.
Not much to say about easylane, most times you just want to make sure you can lasthit inside towerrange, more on that in Carrybuilds. The only thing worth mentioning is that tangos are better on easylane than offlane because you can do sneaky paths that might save your life.
(Take a breath, lot to say about this)
Now this... Is where the magic happens, in terms of itembuilds!
The build of getting early bottle by saving 300~ gold (only bying tangos + 3X IW) was very popularized on SF around 2 years ago. In case you did not see Dendi's guide to solo mid SF I will put a link to it, it's a well made theorycrafting youtubesession where Dendi elaborates some of his thoughts on early bottle among other things.
Back to it- This, people of course realized long ago now, applies to practically all midheroes. Apart from early bottle, I would say that maximumstats is really important on midlane, aswell as early boots.
As you can see, a lot of items are "important early". This means we don't want to waste gold, if you ever buy tango+salve and go mid, only to see your opponent completely ignoring you, then you´re caught wasting 190 gold.
You have first run on the chicken as solomid, that's standard. And if you save gold for bottle, that means you have gold for salve in case you get heavily harassed. With this I mean to say, you can even start a midbuild with 0 HP reg as an investment.
It allows you to get your keyitems quicker and you won't risk "wasting" gold. It definitely takes some getting used to, not having any single hpreg item before lasthitting atleast 5 creeps (along with natural income that should allow your bottle) before going down in the deep red.
If you DONT want a bottle, I recommend aiming at getting boots before your opponent, who most likely wants runecontrol. But if you have boots and he has bottle, he is forced to bottlecrow while you get nice opportunities to gank or be useful in other ways. Finding a haste/dd/invis on the right heroes could be the make-or-break of any earlygame, and I like getting runes for more than just filling an empty bottle.
Carries need to consider what lanepartner they have, what lane they have, and what opponents they are likely to be up against. You never want to miss a lasthit under towerrange. This feels weird to new players, they think this is where it's hardest to lasthit. Incorrect. The tower-area is the safest place on your lane, when your lane is pushed back to tower, you should atleast claim 90% of the lasthits as a carryplayer.
So what is needed in order to be able to do so? You need good maximumdamage, quellingblade is the best item if you expect pulls to happen on your lane (as they normally sets you back inside the tower). As you get better and better at lasthitting you will start getting ashamed every time you DON'T prepare a creep for towerhits. This means you won't have such a need for qb, and the better your opponents are, the higher is the chance that you will need stoutshield for survability.
These guys are quite out of fashion, but that doesn't mean we don't practice them, does it? As a pro player you should be able to play anything at any given time, within your role. I'm mainly a carryplayer, so if I can't play lets say, drow ranger at all then that's a weakness. It's as if a supportplayer can't play WD/Lion/AA/Dazzle, he can only play the standardheroes.
For ranged carries, most are agi so I won't go specifically into INT (Harb/Silen mainly)
but the concept is the same.
Rangedcarries have one great advantage. Earlygame. They are typically a lot more effective on lane, and they don't need to sustain that much damage at any part in the game if their positioning is correct.
Your startbuild, as such, should be very statoriented. Basilius is often a good pickup due to Acquila, saving inventoryslots is a great advantage as you can have lots of cheap items that provide good bonuses.
For a potm/morphling I would recommend the following build:
Slippers (150) Tango (240) 3X IW (399) as default. Then you mix in depending on your plan for midgame. If you want to rune a bottle you don't need to buy more! 200 gold in the bank means you have bottle after the first 2 waves with good lasthitting. If you want acquila, it's your choice to either go ring of protection first for convenient basilius on lane (sideshop), or going for the more cost-effective circlet. Circlet gives much better stats than a ring of protection, so if you expect any trouble on lane, it's much wiser.
Chicken/Wards/Sentries- Who gets what and why?
This is to some of you completely obvious, but you should know the consequences and reasons for everything we do, so I'll go over it quickly.
One support buying chicken+wards while the other gets sentries+smoke is THE most typical choice right now. 1 year ago it was highly uncommon that you started with sentries, but they have trended a lot ,and for good reasons.
Smoke and Courier are obviously the cheap ones, so splitting them between your two most supporting heroes seems fair. Putting smoke aswell as wards on recharge asap is good for the future, specially smoke which has a really long rechargecounter.
There are exceptions of course , even here! If you run a Chen, he can easily buy wards+chicken+smoke all at once in the beginning, or wards sentries chicken even, it would still leave him with 1 clarity and he really doesnt need to regenerate much while jungling.
The reason he can do this is that chen really peaks at lvl 5-9, and will in most cases only run a single gankattempt prior to lvl 5, as he only has one creep till that point. Only one gank means he doesn't need items until then.
This makes him a good companion for egoistic supporters such as ES or even Tide who wants his manaboots+blink as soon as possible.
Way back we used to run a funky strat where I would play the maincarry and buy chicken (which was 200g) and wards, then pick dualroamers who start off with boots. This was actually ridiculously good in some versions, but roaming has become much more limited competetive dota lately so I definitely don't recommend it. Just to show, there is always room for creativity!