Rolled stat allocation chaos!

Hello! I am going to be starting a Descent into Avernus campaign soon, and I'm going to be playing a human wizard going the evoker route. We did session zero last weekend, and stats were rolled. I'm very happy with my results, but I'm having a hard time allocating the numbers! I took Magic initiate and tough as my starting feats to get some defensive spells and the extra hit points to mitigate the squish factor. I rolled, an 18, 15, 13, 13, 12, 11 for stats. My initial thought, with bonuses, was 11str, 15dex, 14con, 20int, 13wis, 12cha. A wizard's important stat is int right? So straight forward, until I thought of trying 11str, 18dex, 14con, 16int, 14wis, 12cha by changing the bonuses and moving around dex and int. Do I go for the pure blaster build with the higher int and risk dying more easily, or do I take less consistent spell damage for a higher AC and initiative? Help please! 

Having the top stat be int, is good.  Str & CHA can be your dump stats. I like your 1st thought/choice.  So you are good with that one if you do nothing else.

I assume you picked the sage background?  CON is good for both HP and concentration.  You could have with sage do a +2 to con, then your choice for wis/int.  So put in a 18 under INT, and boost it at the level 4 ASI.  Boosting CON might be difficult under ASI, and won't be boosted until level 8 or 12.  So give that a 15, and a +2 so you have a 17,

Plan to be in the back and just suck it up with a mediocre dex.  The other thing is to find a background that does both dex and con boost?

Having an 18 does give you freedom to ignore a boost to that stat.

As a wizard int gives you so much more than dex (save dc,hit bonus etc) and a dead enemy can’t deal damage

Keep 15 dex and take Mage Armour spell, that's still AC 15 which is fine. You can always increase Dex at 4th level if you want. There's also spells that can give more defense like Shield, Blur and Mirror Image. So, the 15 Dex is fine.

However, you're fine to keep Int at 18 until 8th level. While maxing your Int is good, the game is balanced around a 16 stat in early levels, so having 18 outta the gate means you're already ahead of the game. Use that +2 elsewhere or for Dex if you want. 

You can also ask your DM for a custom background (there's rules for it in DMG) to get the +2/+1 or +1/+1/+1 starting stat bonus that works best for you. Or see if your DM will let you ignore the ASI restrictions for your chosen background - if they do, add the background but ignore the ASI and leave blank, and on your sheet directly just click the ability, add the bonus there with a note.

You do NOT want a low save DC.

my solution? criminal. you get good dex, int, alert, and the option for con. good skill profciencies too.

Great stats. I don't hate either of your choices. Starting with an 20 INT is strong, of course, but with an 18 Dex, that's a +4 Mod which will stack with mage Armor's base of 13... but you hopefully shouldn't be getting hit all that often as a wizard anyway.

Something to consider, is what you want to do for feats. Descent o Avernus is for 1-13, which means 2 (maybe 3) feats. If you start out with 20 INT, that makes the +1 INT feats less useful. So think about 2 feats you might want to take.

You can offload the pressure of Stat choices to Orros Mark of Fate (Ebon Tide) and Silvery Barbs (preferably loaded into a magic item).  Those 2 spells can hard carry against big attacks, freeing up your ability to invest in Wis and Cha for better skill use.  High Perception, and the Cha skills if your party lacks a Cha caster.  

My main thought here is that if you're not a Gish, you should never be in melee range or away from Cover.  And a Solid source of THP can go a long way as well.    Which raises the concern as to why you think you need to make your Evoker tanky?  Is your party comp not capable of controlling the field?  With a large enough spell list, you have so many broken spells to work with that can make you difficult to touch.  More so if you know how to abuse the environment.  

As an evoker, you have two things you can abuse.... the ability to make the map a living hell to everyone, except your allies.  Meaning any who gets close to you is automatically in Fireball range, and you don't have to worry about hurting allies.   Second, if you're gonna be on the front lines for whatever reason, you're a prime candidate for being a Backpack Wizard.  Make everything regret being in melee range of the melees.