G'day beavi501,
Without realising it, I had posted the following response to the identical post you had placed in the "Content Creators" sub-forum (which is where this thread really belongs) and which of itself, is NOT a good idea, simply because it is impossible to keep track of more than one post on any given subject, especially when they're in two separate locations. As a consequence, this response, which would have been first, might have been the answer you wanted...
...When confronted with such a problem, I always return to 'the basics'. Firstly, think about the 'object' you're creating. EXACTLY what is it? In this specific case, we are creating an object that appears to be the outside portion of a slice of a sphere that has the 'round' edges sliced off to make it square. So, let' start with a sphere...
...make it larger in diameter than the 'box' and align it so that it's center is the same as the center X and Y coordinates of the 'box'. Adjust the Z co-ordinate so that only a portion of it appears above the top of the 'box' and so that the outside edge of the sphere just touches each of the four corners of the 'box'. You may find it easier to to this by making the object "see through"...
...now, if we look carefully at the original 'telephone box' we notice that the roof is not perfectly 'round', it is, in fact, ellipsoid. So, we need to 'squash' or 'stretch' the sphere (in the Z direction) a certain amount to make it look right (I would suggest a 'stretch' of about 150%). Having done this, further adjustments are required to return it to the correct position...
...now we only need a portion of the sphere, so add a "SLICE" modifier to the stack and adjust the location of the 'slice plane' vertically so that it is aligned with the top of the 'box' and, using the 'Remove Top' or 'Remove Bottom' option (whichever is appropriate), eliminate the part of the sphere that is not needed...
...readjust the 'center pivot' of the sphere so that it coincides with the new shape of the sphere (just for convenience)...
...add another "SLICE" modifier to the stack. Rotate the 'Slice Plane' of this modifier only, so that it is vertical and adjust it so that it lines up horizontally with one or other of the edges of the 'box' and vertically so that it slices through the sphere. Using the 'Remove Top' or 'Remove Bottom' option (again, whichever proves to be appropriate), remove the portion of the sphere that is not needed...
...repeat the above step for each of the other 'edges' of the 'box', rotating each 'Slice Plane' appropriately. You will need to alternate between the two options ('Remove Top' and 'Remove Bottom') to obtain the desired effect from one side of the 'box' to the other. Ultimately, you will have five instances of the 'SLICE Modifier' in the stack. Now, you can collapse the stack...
...there are now two options to take, either you can 'shape' the top edges of the 'box' to match the edges of the sphere (using several instances of the 'chamfer' tool) or you can extrude the edges of the sphere to make them match the top of the 'box' (which I think is the better of the two)...
...when you're done, I would "attach" the two objects and weld any relevant vertices...
...In future, try not to place more than one 'copy' of a thread...
Jerker {

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