For most homeowners associations, board members are required to discuss association matters like this at a properly noticed board meeting. That means you need to send out a notice of the board meeting to all residents along with the agenda for the meeting. Then, at the meeting, you can discuss and vote on the items on the agenda. You will, of course, need to establish a quorum at the meeting.
Board meetings usually take place in person (that was the norm prior to COVID). But, depending on state laws and your bylaws, you may be able to hold board meetings electronically. But, again, these meetings require notice and homeowners must be free to attend them.
As for the roof project itself, your HOA should have a separate reserve account set up for this kind of thing. If you don’t have one, you might need to increase assessments this year or levy a special assessment.
Hope this helps and good luck.