Firstly, you are not allocating a “block of T*“. You are allocating a “block of T“.
Secondly, if your T has non-trivial constructor, then until elements are constructed, your block is not really a “block of T”, but rather a block of raw memory. There’s no point in involving T here at all (except for calculating size). A void * pointer is more appropriate with raw memory.
To allocate the memory you can use whatever you prefer
void *raw_data = malloc(num * sizeof(T));
or
void *raw_data = new unsigned char[num * sizeof(T)];
or
void *raw_data = ::operator new(num * sizeof(T));
or
std::allocator<T> a;
void *raw_data = a.allocate(num);
// or
// T *raw_data = a.allocate(num);
Later, when you actually construct the elements (using placement new, as you said), you’ll finally get a meaningful pointer of type T *, but as long as the memory is raw, using T * makes little sense (although it is not an error).
Unless your T has some exotic alignment requirements, the memory returned by the above allocation functions will be properly aligned.
You might actually want to take a look at the memory utilities provided by C++ standard library: std::allocator<> with allocate and construct methods, and algorithms as uninitialized_fill etc. instead or trying to reinvent the wheel.