Creating a set of letter tiles for your language can be done a few ways, including some very easy ones. Creating tiles using paper or cardstock can be a cheap and easy way to make your first set or test your design. You can determine how many copies of each letter to create by deciding yourself, or by using a sample of words and a spreadsheet formula to determine how common each letter is - it's up to you which approach you take.
In English, the letter "A" is much more common than the letter "Q", so in a tile game you would create more "A" tiles and maybe only one "Q" tile. This would apply to your language too. Perhaps "Ŧ" is more common than "Ȼ" or "ʔ" or "λ". Creating a game with letter tiles that proportionally represent your language can make it more natural to play.
I started with a sample of a few thousand words, then ran it through a Google Sheets formula to determine how common each letter is. There's a couple things to consider when choosing words for your sample. If you include full sentences in your sample, the little words like "the" or "in" or "a" will be included, in English we have lots of "definite articles" which would skew the results of how often letters would be used since you can't really play short words like "a" or "or". When choosing sample words you could also consider choosing more beginner words so that beginners might more easily play.
Using Google Sheets, I laid out the letters for SENĆOŦEN in order in one column starting from the top. "A Á Ⱥ B C Ć Ȼ ..." Then in the column B I entered a formula like this:
=(LEN(JOIN("", [Your Sample])) - LEN(SUBSTITUTE(JOIN("", [Your Sample]), A2, "")))
[Your Sample] - In your formula you replace this with the selected range of words you would use in your sample of words from your language.
A2 - Replacet this with the location of the letter you would be finding the frequency for. The formula would output how common each is. Copy this formula in each cell beside each letter of your alphabet.
Once you have a list of letters and how often it comes up, you can calculate the ratio of each letter. For example if you have 600 letters in your sample and "A" is 60 of them, then 10% of your letters should be "A". I would suggest making 100 or 144 tiles, or somewhere inbetween. Using the same example, this would mean that 14 tiles out of 144 would be "A".