80% of the time i usually forgo frozen heart, while the stats/passive are nice, the mana is just not needed on leona
THE KEY is to build hp and max W
Her w scales from armor/mr meaning a point in either is worth more to leona, meaning hp is harder to come by and far more valuable.
With either build i start 
first back
, upgrade to
,
(will need around 1100, adc should have 1550 by this point).
Build revolves around leonas all in. If i feel that we are going to stay lane phase or are at all ahead, i go
ahead and finish after stone/boots
While it does have nice very sustain, gold farm, and a great health boost its the active that really shines botlane, and especially with leona
UNIQUE – DEADLY PHALANX: Shield target ally for 10% of your maximum health for 4 seconds. After 4 seconds, the shield explodes, dealing (100% of the target's AD) + (30% of the target's AP) magic damage, regardless of if the shield remained intact (60 second cooldown).
Basically this is another leona w, with a little more punch. It can be self cast and stacked with w for massive damage or put on your adc for a sure sustain in the fight, an underlooked active.
My second build mirrors my first just without maxing relic until later
for the mr/speed and the armor/hp on deadmans, the 75% slow works very well with leona and the rest of the passive is just a great bonus. Then
and depending on how much ap damage they are doing( usually much more than ad) i will go
to put my hp at an insane level or if i feel im tanky enough in the hp department ill go 
So usual build is something like
maybe
With full build being
{{item:3065}or
or
try it out once i need to get back to abusing relic active myself