Piano roll

MuseScore already has a piano roll interface - try right clicking any measure and choosing it from the menu.

However, you may find it is too limtied for your purposes. MuseScore is a notation program, not a sequencer, and its features are geared around that fact. So you can't just arbitrarily enter notes at any time position, etc - it's more about tweaking aspects of existing notes in standard notation. If you are not comfortable writing in standard notation, maybe better to just use a sequencer in the first place, save the results as a MIDI file, then import that and tweak as needed to get readable results (which would also be required even if there were a more full-featured piano roll within MuseScore - piano roll is not notation and any automated conversion will by necessity require lots of cleanup).

To (maybe) echo what Marc said ... (IMHO™) ... "in this world there are =music notation= programs, and there are =sequencer/DAW= programs," and, although software authors in both camps will certainly 'cross over' to a certain extent, "NEVER the twain shall meet!" :-)

And here's why: "a music-sequencer program" fundamentally deals with "a time-definite sequence of musical events," with "musical notation of that time-definite sequence" being "a nice-to-have APPROXIMATION." Whereas "a music-notation program" fundamentally deals with "the printed page," with "a playback of the content of that printed page" being, once again, "a nice-to-have APPROXIMATION" (albeit of an entirely different sort).

You simply cannot "fully satisfy" both objectives at the same time. One is "time centric," at the expense of symbology, while the other is "symbol centric," at the expense of a timeline. This "impedance mismatch" is intrinsic to both musical tasks. Which is why both types of programs are used ... in parallel.