[atcsleepy]

The correct way for clearance delivery to give you that clearance is

Sandman, clearance delivery, cleared to (intersection) via radar vectors, climp to and report reaching vfr-on-top, tops reported (altitude) or no tops reported, if not on top at 4 thousand, maintain 4 thousand and advise. maintain vfr-on-top. departure frequency xxx.x, squawk xxxx.

tower should give you an initial vector or a proceed on course. approach should also give u a vector to that intersection if the tower doesnt provide any vectors. i can see the tower not giving u vectors if there are specific departure routes in place for your airport or if there are procedures in place between the tower and approach control for departures. either way, you need a vector at some point.

NOTE-
1. When an aircraft has been cleared to maintain
“VFR‐on‐top,” the pilot is responsible to fly at an
appropriate VFR altitude, comply with VFR visibility and
distance from cloud criteria, and to be vigilant so as to see
and avoid other aircraft. The pilot is also responsible to
comply with instrument flight rules applicable to the flight
(e.g., adherence to ATC clearances).
2. Although standard IFR separation is not applied,
controllers shall continue to provide traffic advisories and
safety alerts, and apply merging target procedures to
aircraft operating VFR‐on‐top.

you are on an ifr flight. once you reach vfr-on-top you need to tell the controller. you will then get cleared to maintain vfr-on-top. at that point you are responsible to fly at a vfr altitude and fly vfr while still listening in for instructions like "maintain vfr-on-top between 3000 and 7000". at that point you can think of yourself on flight following but still on an ifr flight plan.

if you happen to get to 4000 and have not reached vfr-on-top, you need to stay at that altitude, advise of your situation and youll get more instructions from there.