How to know if there is no possible space on board to spawn.

I have a method that spawns 4 different type of prefabs in order of priority. it spawns the first type, then spawns the next if there is room. There’s a number, of objects per type to be spawned, specified. I want it done in a way that if there’s no room for an object of lower priority to spawn, then it doesn’t spawn. This is the method I have:

void Spawn( GameObject obj, float height, int num, int max){
	currentObjectsOnBoard = 0;//number of specified objects spawned
	for (int i = 0; i < max; i++) {

		if (num == 0) {

		float x = Random.Range (startX, (startX + boardW));
		float y = height;
		float z = Random.Range (startZ, (startZ - boardH));
		Vector3 temp = new Vector3 (x, y, z);

		Collider[] hitColliders = Physics.OverlapSphere(temp, spacer);
		int a = 0;
		bool free = true;

		while (a < hitColliders.Length)
			if ((hitColliders [a].CompareTag ("Collectable")) || (hitColliders [a].CompareTag ("Obstacle")) || (hitColliders [a].CompareTag ("Hole")) || (hitColliders [a].CompareTag ("Player"))  || (hitColliders [a].CompareTag ("Coin")))  {
				//check if spot is occupied by any of the above, within a radius specified by spacer

		if (free) {
			Instantiate (obj, temp, Quaternion.identity);
		} else {
			i--;//i did it like this so the maximum number of spawnable items can be fully reached

		if ((currentObjectsOnBoard == num)) {
			//if object reaches number specified or if no more can be spawned.

How I implemented this was before each object is spawned, I calculate the maximum number of that object that can be spawned after objects of higher priority have been spawned…I think my problem is my math. I think I’m not calculating the maximum number spawnable right. I use the are of each object assuming this was a flat 2d board and I multiply that number by the space I want in between all objects. Here’s how I implemented the first two:

maxCollectablesOnBoard = (int) (((boardArea- (playerArea)) / (collectArea)));
	Spawn (collectable, collectAndCoinHeight, collectNum, maxCollectablesOnBoard);

	tempcollect = currentObjectsOnBoard;//number of collectables spawned if different from numer requested
	maxHolesOnBoard = (int) (((boardArea  - (playerArea) - (tempcollect * collectArea)) / (holeArea)));
	Spawn (hole, holeHeight, holeNum, maxHolesOnBoard);

here’s an example of how I calculated the area:

collectArea = (spacer+1) * (Mathf.PI * collectRad * collectRad);

I’ve been trying this for days and I can’t figure it out, I’d really appreciate the help. Thank you!

i cant really help u with this based on your script and the way u did it;

if it was on me i would do 2 Instantiation
first one is just temperory and create an object of the same prefab without meshrenderer but has collider ;
this Instantiation has a script on it that works as detector see if it has collision with any thing or not ;
if not it will send a request to the main script and send the order to Instantiate the real object and destroy him self cause its notneeded any more;