Hi Hannah
We have visited DLP twice, once in early September when it was absolutely sweltering, and then January this year, when it was freezing cold!
The weather in Paris is probably a few degrees warmer than the UK but not much difference really. If you want to get the best weather I would aim for June/July/August but even then there is a risk it could be chilly and raining!
Where are you thinking of staying? We stayed at Hotel New York last visit and loved it.
