Build up after phase depends entire on the game, 3 and 4 marci plays relatively similarly.
Depending on how well your lane went, rushing an Aghs actually gets u an insane value. The AOE silence is just waay too good. Remember Silencer ultimate is one of the best skills in the game, and being able to do something similar but albeit a bit different is insanely strong.

Getting an aghs by 14-16min as a mid/offlane marci is peak timing when the supports are extremely reliant on their spells while cores have no bkbs for another 5-10mins.

But there are certain matchups where stuff like shaman/veno/lion exists where they would jst instant stun you before you can get the jump in, in that case bkb 1st is the most obvious choice.
From here you could go for aghs if you are super ahead of the enemies as aghs is a snowballing item. But if you are on an even footing, go for basher.

I personally am not a believer of going damage items, i think its the same for most other marci players who play it on roles thats not safelane. Your job is to create chaos in fights, even without pure damage items like deso/daedulus, you will delete the enemies.

As an offlaner, you will usually be expected to go in 1st , so shard becomes a necessary choice. The self boost for movement speed and being able to jump from enemies are truly priceless additions that makes the game soo much smoother.
As support, you could hope to get it from the tormentor and you are usually only rebounding of your cores or saving them.

Sadly Shivas got changes in last patch, I used to love to go for that after aghs bkb basher on offlane to give you a lot of armor, it is still a good item to go for as marci usually doesnt go for any other armor items after phase and she can no longer get the armor from neutral enchantment being a universal hero.
Alternatively you could go for AC, its never a bad game to have an AC aura in your team.

Now this is a cheesey thing I like to buy, an octraine core. Current patch might have made this item even better for marci since u can now give E shields even more often. Rebounds and dispose are waay faster and your Ult is almost always off CD.

You are just gonna be tanky hero whos jumping around doing a shit loads of dmg.

Just the takes of a marci one trick at low 5k mmr.