Im having doubts that my magicka will be higher than 350 when my intelligence reaches 100 is there any other ways to raise my magicka

Assuming you have a race and birthsign that helps your magicka and that you max intelligence, I think a good thing is to seek transcendent sigil stones (Level +17) that fortify magicka at 50 a pop and use them to enchant several items of apparel.

Are you sure you need to have your magicka higher than 350?

As stated above, enchantments of Fort Magicka can get it up in the 650 range. You can increase it temp, by using alchemy. You can stack the effect by drinking multiple potions. Creating a custom spell with Fort Intel 100 and Fort Mag 100, can raise it another 300. Create several of those, lasting for 30 sec ( or whatever ), with different names, and they will stack. Giving you a temp total Magicka into the thousands.

You asked, and I answered. As far as " why "...Well, if you like playing with custom spells as much as I do. It's the only way you can cast crazy and, not so efficient, spell combinations. Granted there are more practical ways, but I thrive on the non practical, and sometimes idiotic avenues. That's what makes this game great, you have a lot of options.

However, for your first playthrough, it would be wise to stick to the better strategies. Better than listening to the rantings of an old man. :mohawk:

Umm... you do not need to have magicka that high, not even close, even to cast extremely powerful spells.

Fortify Intelligence 100 pts 3 secs + Fortify Magicka 100 pts 3 secs + Drain Magicka 3 pts 3 secs on self will give you 300 magicka to create extremely powerful spells and continuously cast them. Actually, you really never need to use 300 magicka spells and will probably eliminate or greatly reduce the Fortify Int 100 pts. If you couple weaknesses on your spells, you would only need at most two different spells that you alternate casting. The effects will escalate very quickly, far more quickly than anything in the game can survive (aside from the few enemies with Reflect Spell, of course).