Roll a Wisdom (Stealth) check.
I have used this many times before (see below to several answers where I talk about my experience in greater detail). We can use the Variant: Skills with Different Abilities rule to get a better representation of this situation:
Normally, your proficiency in a skill applies only to a specific kind of ability check. Proficiency in Athletics, for example, usually applies to Strength checks. In some situations, though, your proficiency might reasonably apply to a different kind of check. In such cases, the DM might ask for a check using an unusual combination of ability and skill, or you might ask your DM if you can apply a proficiency to a different check. For example, if you have to swim from an offshore island to the mainland, your DM might call for a Constitution check to see if you have the stamina to make it that far. In this case, your DM might allow you to apply your proficiency in Athletics and ask for a Constitution (Athletics) check. So if you're proficient in Athletics, you apply your proficiency bonus to the Constitution check just as you would normally do for a Strength (Athletics) check. Similarly, when your half-orc barbarian uses a display of raw strength to intimidate an enemy, your DM might ask for a Strength (Intimidation) check, even though Intimidation is normally associated with Charisma.
So in this situation, obviously we have elements of stealth. The stealth skill is decribed:
Make a Dexterity (Stealth) check when you attempt to conceal yourself from enemies, slink past guards, slip away without being noticed, or sneak up on someone without being seen or heard.
Stealth is typically a dexterity check because that is usually the attribute that makes the most sense - can you step lightly and move quickly at the same time. But your situation is a little different. We aren't trying to be as quiet as possible, or move quickly and stealthily. We are trying to find the best hiding spot in the environment. Wisdom checks are described so:
A Wisdom check might reflect an effort to read body language, understand someone’s feelings, notice things about the environment, or care for an injured person.
So in this situation, we are combining our knowledge and skills of hiding with noticing things about the environment so these two things can work together: Wisdom (Stealth).
I explain the calculation for this in my answer here: Variant: Skills with Different Abilities confuses me, and I give some general advice about the rule here: How does the Variant: Skills with Different Abilities rule affect the game?
, and give more context about how I use this rule here: What are the mechanics for hiding something that is not yourself?