does anyone have a suggestion?.

Like legit ugly(art design) or by the standards of the story?

For traditional romance you could try Hatsukoi Gentei. It has the class supermodel falling for Mr. "frogface" much to her consternation.

For something dark and twisted in the horror genre you could try Saiteihen no Otoko

I think 3D Kanojo fits the bill

Try "Monkey High"/

Oddly, it's shown here as having only one chapter scanlated, but it can be found fully scanlated in the usual places.

The guy is not ugly, but he's short and nobody's idea of a dreamboat. The story is very refreshing for that reason.

And, similar to "Monkey High" in having a decidedly non-handsome male lead, try "Sundome". Sundome is a real find. At first it seems like ecchi nonsense, but it grows on you.

Ahiru no Ouji-sama Maybe... I dropped this some time ago, but I remember that the main girl started dating an "ugly" guy.

it doesn't matter

If you don't mind oneshots, definitely check Debu to Bijin (The Beauty and the Fatty).

Maybe try Angel Densetsu, it's a comedy manga, but the romance part is still there. The MC is scary-looking, described as a drug-addict, a delinquent or even a demon.

There's also Ore Monogatari!!. The main character isn't exactly ugly, but he's definitely not the type most girls would fall for.

RaButa

~4400 manga completed
~1700 ongoing...