I had a flat roofed motorhome about 10 years ago. I didn't like the flat roof. It collected a lot of water. Parking off level kind of contradicts what the refer manufacturers tell you.
The motorhome had trim all the way around the roof edge that kind of formed a lip. Water would collect behind that lip and be about 1/4" deep. Never leaked but keeping it clean was out of the question. even if it didn't rain it would collect the air conditioner condensation.
I don't have any first hand knowledge of Lance RVs. I did look at them when we were shopping and a lot of the components looked kind of cheap to me. I guess they use a lot of light weight stuff (like plastic windows) to keep the RV light. I'm not concerned about weight that much.
I wouldn't have a flat roofed RV these days. No advantage to it and several disadvantages.
When seconds count, the police are only minutes away.
2019 Newmar Canyon Star 3627
2017 Jeep Wrangler JKU