A few ways to do this...

Rosheen front and center:

• Ramp into splashy spells like hydras, fireballs
• X artifacts

Rosheen as support card:

• lands matter; landfall, awaken, scapeshift, recursion...basically an omnath deck in disguise
• spellslinger/storm
• symmetric ramp, asymmetric payoffs; use mana more efficiently than anyone else via X spells
• tappy/untappy

X spells/abilities

Meta: How to deal with players who use their abundance of mana to draw lots of cards

A recipe:

• 40 land
• 20-25 ramp/mana acceleration
• 10-15 big draw spells
• 7-10 removal
• 7-10 win conditions
• 7-10 ways to recur/protect boardstate