Did a bit of concepting work, tell me what you think.
-All cards are identified by their race (Terran/Protoss/Zerg/Neutral), type (Unit/Building/Addon/Micro/Tech/Misc), and, for unit cards, subtype (Infantry/Armor/Air/Special). (The Air subtype doesn't indicate that a unit flies: A flier will have the word "Flier" below it's picture. I have reasons for this that will be clear once I create a few cards, assuming you want me to do card creation ofc.)
-During your turn, you may tap a worker and a mineral field to move any card from your hand to the field, or any building from your deck to your hand. For the later, you must have certain prerequisite cards on the field (eg. a Barracks for an Academy).
-During your turn, you may tap a production building to move any card it produces from your deck to your hand, assuming you have all prerequisite cards on the field (eg. an Academy for Medics).
-Addons may be placed next to any appropriate structure. For example, a Physics Lab may be placed next to any Science Facility. Mineral Fields count as addons to the CC/Nexus/Hatchery, so if you want a ComSat or Nuke Silo, you'll need to sacrifice a slot that could otherwise be occupied by a Mineral Field.
-The way Spells work is that you must have the appropriate Tech card on the field. Casting a spell requires you to tap the unit that casts it. If you have the appropriate "Reactor" card on the field (eg Caduceous Reactor for Medics) the unit is not tapped if you get a "6" on a 6-sided dice.
Some card ideas I had:
-Depot Wall: Terran micro card. Makes all buildings excpet targetted Supply Depot untargettable by non-fliers.
-Psi Distruptier: Terran building card. Zerg micro cards may not be played as long as it is on the field.
-Sarah Kerrigan: Terran infantry unit card. When she dies, you may play an "Infested Kerrigan" token (which is much stronger than Sarah Kerrigan) on the field.
-Worker Scouting: Neutral micro card. Tap a worker to reveal one card in the opponent's hand.
-Overlord Scouting: Zerg micro card. Reveal one card in the opponent's hand.
-Parasite Kakaru: Zerg micro card. Play one "Parasited Kakaru" on the field. Each turn, reveal one random card in the opponent's hand for each "Parasited Kakaru" you control.
None.