Anyone know of a platform I can use to create a CRM system for business owners?

Hi all,

I’m looking to create a CRM app for general contractors. One app I’ve seen that’s a good example of what I’m trying to create is Jobber.

So far I’ve come across CRM app builders such as highlevel & zoho but I think these apps I’m creating are solely for MY business.

My goal is to create a CRM app available in app stores so contractors can download it and keep track of jobs, take customer payment etc.

Can anyone point me in the right direction as far as online app builders for my situation or is this something I’m going to have built from scratch?

Edit for more info: I would not manage the app for these companies. Business owners with admin access can add/remove supplies edit costs etc. Their employees would be able to see what job sites they are working, a list of tasks to be completed, and the ability to mark jobs as closed once work is done.