As I look through the XML I found this curious problem with the road building ability

<AbilityBonus InternalName="RoadBuildingAbility">
    <AbilityBonusType>Unit_Design</AbilityBonusType>
    <AbilityBonusOption InternalName="RoadBuilding">
        <DisplayName>Road Building</DisplayName>
        <Description>Allows the unit to build roads</Description>
        <Icon>Ability_PathOfTheGovernor_Icon.png</Icon>
        <GameModifier>
            <ModType>Unit</ModType>
            <Attribute>UnlockAction</Attribute>
            <StrVal>BuildRoad</StrVal>
            <Provides>Allows the unit to build roads</Provides>
        </GameModifier>
          <Cost>10</Cost>
        <Type>Army</Type>
        <Prereq>
            <Type>Race</Type>
            <Attribute>Race_Type_Mancers</Attribute>
        </Prereq>
        <AIData AIPersonality="AI_General">
            <AIPriority>5</AIPriority>
        </AIData>
     </AbilityBonusOption>
</AbilityBonus>

This cost has no effect for the actual unit design. I assume that it was intended to have the following line instead:

        <AdditionalTrainingTurns>10</AdditionalTrainingTurns>

currently there is no cost difference when choosing the road building ability.