Warning!This is meant to be a pubstomping build, if you're looking for a competetive build, Figure one out yourself :)
Also expect that my spelling/building sentences isnt the best around(English is my second language!
How do I get good at Isis you ask? The key is to master your Spirit Ball. I'ts the reason you dominate as Isis
So I've been playing Isis a lot and really like her skillset which makes me play good with her. I want to share how I build and play Isis in middle lane!
Here is my stats with Isis and my last games!
I start with Tier 2 Boots of Magi, 2 health potions and 1 mana potion due to Isis passive, You get the mana needed for the while you need to be in lane and after the first recall you should be able to finish you boots.
Mid game is good for Isis, If you get the enemy tower down you can easily push down a lane and leave for a sidelane. With your ulti, you will almost never fail. When comming for a gank be sure to know that Spirit Ball will hit, Spirit Ball is what makes Isis a really good ganker. Make sure that your team know you're comming and stun the enemy the quickly follow up with your silence. Then enemy will not be able do so anyting for 2 seconds with Dispel Magic only leveled up once. After that you can use your ulti for heal if needed or you can use it as damage, it dependes on how the fight tourn out. Just keep in mind that if you're ahead in level your ulti will do plenty of damage to the enemy.
After a gank recall or if you have mana(you usually have mana) Go back to lane and pick up the buffs that are available(you will get ahead a ton if you master picking up buffs on the way to lane. Pus your lane and head for the next lane and do it over and over again. Isis is really easy to rotate with. If you got a lot of mana keep in mind that your Wind Gust gives you movementspeed.
This is where Isis can be really fun to play. Getting people cought with Spirit Ball and then finish them off with your ulti without them almost not even noticing you is so awarding and hilarious. Wards are your best friends and being able to shoot them through walls and see them and to know when exactly to detonate is key. Spirit ball is what makes you strong in jungle.
This is when you and your team are going to teamfight. You can control fights easy if you're fed. Be sure that your team is following you and as soon you hit a stun the team should follow up on it. If your team meets trouble you have your ulti that can completly change the looks of a teamfight. With a stacked up ulti you will be able to heal a great amount and deal deadly damage at the same time, be sure that your tmea understand what a powerfull heal you have and that its okay to go fight.