Yank out that old Statics text.  Get the yardstick (non bendable measuring
device usually made of wood 'meterstick' in metriclands)  Get a soft pencil
#1 will do.  Get some removable tape (drafting tape) Scotch blue masking
tape. You are going to figger out where to place the ends of those struts.
First you'll need to decide how long the strut should be.  (Kim uses 40",
McMaster Carr stocks a 27 and many other sizes.)

Recalling that the strut has a minimum (collapsed) length and a maximum
(extended) length you can approximate the locations by using your yardstick
to find locations that will allow almost full extension and almost full
collapsed lengths.  The extended length is that length measured when the
roof is in it's "upright and locked" position.  The retracted length is the
distance between the mountpoints when the roof is down.

I would start with the retracted length and

You need to approximate the weight of the loaded top.  You can do this by
weighing it with an overhead spring balance (imagination comes into play
here).  Once you know the Loaded and the Empty weights  as mounted on the
roof, you have the boundary conditions for the lifting  parameters.  Much
easier to just measure the weights as mounted on the roof rather than try to
calculate the geometries and equivalences.

NB the roof is hinged at one end so it's not a 'dead' lift.  You will need
to know how much force it takes to raise the front edge of the roof when
loaded.  This force decreases somewhat as the roof is raised. (geometry
again)  You can do the relevant center of mass calculations and predict the
lifting force but it's likely easier to just measure.

EG:  If it takes 100lbs of lifting force to raise the loaded roof from the
front and it takes 50 lbs to raise the unloaded roof from the front, you
have the end points of the exercise.  Looking at the geometry and moving the
lifting point farther to the rear so as to allow the use of a 27" fully
extended strut you can arrive at various solutions with respect to mounting
points.  Each solution will have differing lifting forces because of the
position of the roof mounting point.