We really need to see a photo of the conditions. If you're in snow country, you want to avoid a flat roof.

Talk to an architech.

The two roofs. I am not concerned about trhe skylight or the deck. They can easily be taken out.

I think the house looks very nice just like it is, with the exception of the brick, that appears to have been painted.

Where the two roofs meet is called a Valley. This intersection is always more prone to leaks.

You could simply convert the two roofs into a HIP Roof.

Then there is this famous style Hip Roof.

Turning two pyramid roofs into a flat roof is a full structural project, not a re-roof. The existing roof framing has to come off and new flat joists sized for the span and the snow load go on, so plan on an engineer, permits, and tying the two sections into one continuous structure. Since you're in snow country, a truly flat roof also needs tapered insulation or crickets to give it slope, plus a membrane system with drains that won't ice-dam. In most cases converting both sections into one clean hip roof is cheaper, still sheds snow, and looks intentional. Before you make an offer on the house, get a framing contractor to price both options — the answer might decide the house for you.

Anything can be done with enough money. The picture must have been changed, but what is posted looks like 2 separate massings but close, or an addition that doesn't mirror the original house fully. And then there is a deck overlook, and if the "cupola" on one roof is functional (e.g. a vernacular cooling tower say in Hawaii - a username is not an assumption of where this is, or I'd live in a tree) those may both want to continue being there is some fashion. So you can top off and have a flat roof, and flat roofs are everywhere and anywhere, it has nothing to do with snow or water. The roof may not be continuous across the entire house, maybe it's both a pitched and flat roof, maybe you want to build a seating area up there, there is just not enough information. But the most important criteria for any house is location, location, location.

This could be a substantial alteration, so I’d make feasibility part of your purchase decision rather than treating it as a roofing estimate.

Have a local architect and structural engineer assess the existing framing and compare a low-slope conversion with a revised pitched-roof option. Ask for preliminary construction pricing that includes demolition, weather protection, structural changes, insulation and drainage—not just the finished roofing.

A ‘flat’ roof still needs designed drainage; its appearance and its construction are separate questions.

Where is the house, and what bothers you most: the two roof shapes, their height, or the overall appearance? There may be a way to achieve your goal with less reconstruction.

I read this mistaken assumption all the time on Houzz. "Flat" roofs are not perfectly level. They have a pitch and that is given with use of that term. A flat or low slope roof is defined as having a pitch less than 3:12. No roof in the history of roofs has probably been perfectly level.