You'll need to be more specific when you say make it from Reborn's engine. Reborn is not a ROM hack but a fan game (like Insurgence, Zeta/Omicron, Uranium and so on).
Pokemon Reborn is made using RPGMakerXP (a program made by enterbrain that can be bought for around $30). Pokemon Essentials is a scripts/ graphics/ sounds package that works inside of RPGMaker and can be downloaded for free. All of these things can be used by anyone and used pretty easily. If you need a tutorial on how to make your game with these two things I'd look up the series by AtomicReactor on youtube which will cover the basics.
However, you cannot (and it isn't practical to) take the maps used in Reborn and just cover them over with other tiles and change the events. With credit you can use some of the game's graphics and scripts but not the game itself.
When Ame completes the game she will open it to user mods (e.g. changes of difficulty of Reborn itself).
So pretty much- you can use the same tools as Ame and some of her resources but you can't build your game off Reborn itself (this would be much harder and more limiting anyway!).
You can download pokemon essentials here: http://pokemonessentials.wikia.com/wiki/Pok%C3%A9mon_Essentials_Wiki