Can't Romance Sera

How far are you in the storyline?

Your class and race act as modifiers. Sera is significantly easier to romance as a qunari warrior/rogue than as a dalish mage. That's why in some playthroughs you can start a romance shortly after reaching Skyhold, while in other playthroughs you need to porgress much further.

I'm about to start the quest Wicked eyes and wicked hearts. I'm a Female, human, Rouge and I've made very possible choice to gain the most approval possible. Its also worth mentioning that this is my second play through. in my first play through i beat the game and she never gave me the option to romance her. Just kept saying we need to travel around more.

What system are you on? If PC, are you using any mods? If so, what?
Sera doesn't like to share, so if you're even a little bit in a relationship with someone else, she might decide you're taken and that's that. 
Also, choosing the choices to gain the most approval possible means you're not always choosing the romance choices, which means the game thinks you're not interested.
If she wants to travel more, then do that. After a while you should be able to talk to her about it again. If you're only starting the Winter Ball quest thing, you're not all that far in the game, so you mightn't be able to get super far in the romance (can't remember what you can do when).
If you're at max approval with a follower, it seems they stop gaining more approval when you do things they like (not sure about this, it's just what I've observed in my playthroughs). You can still lose it, however.
You can also try a repair of the game if all else fails. Pretty quick and easy to do.

OK, I now can't even read what I've written, so I'm gonna leave it there. 😛 Good luck.

I'm playing on PC with no mods. I've flirted with Cullen once or twice but did not try to start a romance with him. i always picked the heart/romance option with Sera. i tried a repair, no change. im still playing and im almost at the final mission, still can't romance her. i know i would be able to romance her as a qunari but i don't want to do that. Maybe i cant flirt with anyone at all? i don't know, that would be weird if that's the case.

You can romance Sera as a female of any race, I think it's just harder as an elf (especially if you're too "elfy"), easier as a Qunari or Dwarf. Possibly harder as a mage. 
You should be able to flirt with any viable options (and in some conversations, Cassandra and Dorian if you started flirting with him and didn't tell him to stop after the quest with his dad), unless you're flagged as being in a relationship with someone.
If you want, you could send me your save file and I'll have a look at the flags in the editor, see if anything looks hinky. 
Have you done Sera's quest involving a war table mission and a trip to meet a 'friend' for a reward? Have you gone on a pranking spree with her? Had gross cookies on a roof? 

If you go through the game just doing main quests instead of going off onto optional maps and returning to Skyhold, you are likely to miss a lot of interactions with the companions (as some of them require you leaving Skyhold and returning again to activate between main quests), so that could be a reason you're not able to romance anyone, maybe? You'll also miss methods of changing their approval ratings, as there are things you can do in certain areas (as well as people to judge) which are completely missable if you just stick to the main quests.
I run around every time I get back to Skyhold (largely trying to get Cole's 'odd behaviour' things to pop up, which they seem to randomly decide to stop doing in some playthroughs) and talk to everyone, so I've never had similar issues. 

 I've done both quest and the pranks and the cookies scenes. I'm a completionist so I've done all most all side quest and explored a lot with her. i got 150 influence. I'm close to the end of the game now. i will try to get as close to the end as i can finished the remaining side quest and see what happens then. Thanks for the help so far. i tried to send my save file my it wont go through.

If you really want to send the file, you could probably host it on a free file sharing site (something like dropbox or rapidshare) and PM me the link, I guess. Didn't realise there was no option to attach a file to PMs like there are to posts. 
And yeah, by what you've done, you should certainly have been able to romance her long before now. How do you know how much influence you have? Only way I know of to check is the save editor.

I have a Qunari mage and a Human Rogue who are Virtually at Wicked Hearts, with all else done on Max approval, having roof time and NO flirts apart from Cassi 😛

---

@godofdragonage1 wrote:
Eww why would you want to ugliest female npc aside from the baldie lol well IMO

---

Quality post!

Probably because of her personality.