hi we play with the variant rule of roll the HP but i got a lot of 1, so exist a limit of minimim HP i can have i starting to feel underpower.

Usually, even with the variant rule, most people go with the maximum at first level to get the character off on the right foot and then roll for every level after that. Even then, it is common for the option for the player to be able to choose between the roll they got and the standard average number, whichever is higher, giving even bad rolls a hard minimum of "average."

but my DM say that he only want use the roll like in 3.5

If I ever make players roll for HP, I'd make the average HP value the minimum value, so any result rolled below the average for the die becomes the average.

The last DM I liked that did rolling dice, you got the standard half dice for free, and you roll the other half.

I think 1HP roll are B.S.  Even my most OG DM allowed a reroll on a 1.

Even in 3.5 you could just take Standard HD and rule was max at 1st level.

I did that with a Dwarf Wizard.  I roll a 16 and 18, but the 18 in Con and became a Dwarf... 20 Con, I had 1d4+5 EVERY level.  I had more HP then our fighter.

GM still killed me before my first initiative in a combat.

I'd play it similar honestly -- but the rule is max hp at level 1 (that i would never change).  I give my players the choice, take the average or roll, but if you roll, you can't now decide to take the average, you are stuck with it.  Otherwise, what's the point of rolling?  If you get worse than average and are allowed to reroll it, wouldn't everyone just do that to ensure that they get a chance at higher than average? 

I also let my players make the decision at every level, so they could roll at level 2 and theoretically get a 1, then if they survive to level 3, they can take the average if they don't want to risk it again.  A few of my players took the average at level 2 and 3, then rolled moving forward, so that they got a good base.

But as StormKnight said, that's up to your group and your DM.  We can guide you to the rules, but we can't enforce them for you/your group.  

One way to increase your HP outside of your rolling each level is to take the "Tough" feat instead of an ASI, which gives you an extra 2hp for every level you have, and every level you gain moving forward; if of course, your game allows feats

Quote from Mehetmet >>

I'd play it similar honestly -- but the rule is max hp at level 1 (that i would never change).  I give my players the choice, take the average or roll, but if you roll, you can't now decide to take the average, you are stuck with it.  Otherwise, what's the point of rolling?  If you get worse than average and are allowed to reroll it, wouldn't everyone just do that to ensure that they get a chance at higher than average? 

I also let my players make the decision at every level, so they could roll at level 2 and theoretically get a 1, then if they survive to level 3, they can take the average if they don't want to risk it again.  A few of my players took the average at level 2 and 3, then rolled moving forward, so that they got a good base.

But as StormKnight said, that's up to your group and your DM.  We can guide you to the rules, but we can't enforce them for you/your group.  

One way to increase your HP outside of your rolling each level is to take the "Tough" feat instead of an ASI, which gives you an extra 2hp for every level you have, and every level you gain moving forward; if of course, your game allows feats