Germany, France, and Italy Itinerary Help

How long is the trip (including travel days)?

How many nights do you planned for this trip? There are some long transfer here (Paris to Munich for example) that might better be done by plane. Since you are focused on Oktoberfest, perhaps you can give us a date range so we can figure out if it is more efficient to start in Munich or Paris.

I hope that this trip is for at least 3 weeks to cover 5 destinations including 2 of the biggest hitters in Europe, Paris and Rome. You are going to lose at least half a day every time you move destinations.

Where you start and end depends more on where you can fly into/from rather than the costs once you are in Europe.

Fly between France and Italy and take the train within Italy.

Go to the "rome2rio" website (https://www.rome2rio.com/) and plug in the destinations you want to cover. It will tell you how long the travel time is and give you a range of cost so you can compare. You can fly to Rome, train to Florence, train to Venice, fly to Munich, fly to Paris and go home from there. If you tell us how many nights you plan to travel you could get more specific advice.

Chances are you're trying to take on too much moving around.
Germany, France and Italy are worthy of a full European trip each. They are all great countries and there's so much to see in each. Transportation between Munich and Paris by train or plane is also not easy--politics involved. It's pretty far on the ground.
Oktoberfest is an incredible time to be in Munich, but rooms are difficult to find and very expensive. The name is also misleading because it barely goes into October the first weekend. It's about as easy to stay outside of the city and take a train in to see the festival.

Sorry everyone, I should've been more specific. We're planning on being there 10 days.

We would only like to go to Germany for Oktoberfest so one day in Germany would be enough. We would like to spend the rest of the time in Italy and France.

Does the 10 days include flights? You lose a whole day getting there, and the first day or two with jet lag.

12 days total. 10 days to travel within those countries.

You'll lose most of the day moving from one hotel to another in another city. Assuming you travel open-jaw, that's 4 days, 5 days otherwise. The first day you'll probably be slowed to some extent due to jetlag. That doesn't leave much time to see what you've planned, five cities plus O'fest in 5 days.

Going to places like Paris and staying only one day is kinda like going to the SuperBowl and leaving after the initial kickoff. That much moving will also may be quite tiring.

To hit all the destinations you list, the best I can offer is to fly into Paris/ train or fly to Munich*/ fly to Venice/ train to Florence/ train to Rome/ fly home OR do it in reverse.

(* Its pretty much a toss up cost and time wise of train vs plane)

Given the time you have it appears you have 2 too many destinations you are trying to get to. That's my $0.02

1 night Munich
fly to venice - 2
train to Florence- 2
train to Rome -2 or 3
fly to Paris - 2 or 2

rushed but you can get the highlights. not too much different than i did when younger